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Home My WebLink About1997-05-13 - AGENDA REPORTS - SEISMIC HAZARD FOR ELSEMERE CY (2)AGENDA REPORT City Manager Approval Item to be presented by: Don Williams CONSENT CALENDAR DATE: May 13, 1997 SUBJECT: SEISMIC HAZARD EVALUATION REPORT FOR ELSMERE CANYON DEPARTMENT: City Manager In 1995, during the City's review of the Draft Environmental Impact Report/Environmental Impact Statement ("DEIR/S") prepared for the proposed Elsmere Canyon landfill, it was determined that some seismic information in the DEIR/S was inaccurate or incomplete. Additionally, it was believed by the City's seismic engineer for the review, Hushmand & Associates, that the landfill's design standards were based on bad estimates and were therefore inadequate and flawed. Finally, as the DEIR/S had been prepared prior to January 1994, it contained no information reflecting new and relevant scientific seismic data from the Northridge earthquake. A seismic hazard evaluation report was commissioned by the City in March 1995. The evaluation was substantially complete in September 1995, but not final until all relevant seismic information pertaining to the Northridge quake could be incorporated. Hushmand revised the report in December in 1996 when final data became available, and forwarded the report to the City. ANALYSIS The report concludes that the DEIR/S does not adequately evaluate all seismic impacts, particularly the potential for severe seismic -induced ground shaking, on the project. The document fails to recognize the need for up-to-date seismic hazard analysis of the site, including the most recent information available on seismicity, seismic source model, and ground motion attenuation relations developed for the region after the 1994 Northridge quake and other seismic events. Of special concern are acceleration estimates in the DEIR/S which may be off by as much as 100%. The report concludes that the state standards for landfill construction originally proposed by the proponent are inadequate and unacceptable. A full copy of the report is available in the Council's reading file. RECOMMENDATION Receive, and direct staff to forward copies of the report to the County of Los Angeles, the United States Forest Service, and other interested parties. 51CCAGENDAV SMSHZ.R" npp�qgg A enda Item:� SEISMIC HAZARD EVALUATION FINAL REPORT PROPOSED ELSMERE CANYON LANDFILL Prepared for City of Santa Clarita 23920 Valencia Boulevard, Suite 300 Santa Clarita, CA 91355-2196 Prepared by Hushmand Associates Geotechnical and Seismic Engineers 17752 Skypark Circle, Suite 285 Irvine, California 92614-6419 September 1995 (Revised December 1996) Hushm and Associates Geotechnical, Environmental, and Seismic Engineers December 13, 1996 City of Santa Clarita 23920 Valencia Boulevard, Suite 300 Santa Clarita, CA 91355-2196 Attention: Mr. Donald M. Williams Subject: Final Report for Seismic Hazard Evaluation, Proposed Elsmere Canyon Landfill City of Santa Clarita PO # 10969, Dated 5-9-95 Dear Mr. Williams: In accordance with your request and authorization, Hushmand Associates has completed the seismic hazard evaluation of the proposed Elsmere Canyon landfill site located south and east of the City of Santa Clarita, approximately 0.5 mile northeast of the existing State Route 14/Interstate 5 (SR/I-5) interchange. This evaluation was performed upon your acceptance and authorization of our proposal, dated March 9, 1995, prepared for the City of Santa ClariWs main contractor, The Gibson Company, for the review and evaluation of the Elsmere Canyon Landfill EIR/EIS documents. The project work was also performed according to the terms of the City's Purchase Order Number 10969. The scope of our work, as outlined in our proposal dated March 9, 1995, included a probabilistic seismic hazard analysis to evaluate the site acceleration for the earthquake with 10 percent or higher probability of occurrence in 250 years (approximately the earthquake with 2400 -year return period) which is defined as the design earthquake in Subtitle D of the Federal Code of Regulations. Preliminary results of the analysis were presented in Dr. Hushmand's Oral Testimony Script during the May 31, 1995 Elsmere Canyon Planing Commission Hearing. As mutually accepted, following the planing commission hearing on May 31, 1995, final results of the study, after inclusion of the most recent information from the Northridge earthquake research projects and additional independent seismic hazard analysis by Dr. Norm A. Abrahamson, an internationally known seismologist, were 17752 Skypark Circle, Suite 28S - Irvine, California 92614 - (714) 474-233S - Fax (714) 474.85S8 Final Report- Elsmere Canyon Seismic Hazaru r.valuation Page 2 documented in this written report. In particular, results of a study by the California Division of Nfines and Geology (CDMG) on the seismicity of the Los Angeles, Ventura, and Orange Counties in southern California, published in the February 1996 issue of the Bulletin of the Seismological Society of America, were included in our final report. After the 1994 Northridge earthquake, the CDMG was commissioned by the Governor's office to provide a model of the faulting and seismicity of the southern California to be used as a guide in future seismic hazard analyses in the area. If you have any questions regarding this report, please do not hesitate to contact this office. We appreciate this opportunity to provide our professional services to the City of Santa Clarita. Respectfully submitted, HUSHMAND ASSOCIATES H0. C 044777 m 0* 3-31-98 a Ben Hushmand, Ph.D., P.E. 44777 President MMIREPORTS Please also note that our address has recently changed. The new address is: Hushmand Associates 17752 Skypark Circle, Suite 285 Irvine, CA 92614 TABLE OF CONTENTS 1.0 INTRODUCTION ............................................................ I 1.1 REGULATORY REQUIREMENTS ........................................ I 2.0 FAULTING AND SEISMICITY ................................................. 3 2.1 GENERAL ............................................................ 3 2.2 TECTONIC SETTING ................................................... 3 2.3 FAULTING AND SEISMICITY ........................................... 4 2.3.1 FAULTING .................................................... 4 2.3.2 SEISMICITY ................................................... 5 3.0 PROBABILISTIC SEISMIC HAZARD EVALUATION ............................... 6 3.1 APPROACH .................. * .... * .... *'***** ..... * * ... * * '' 6 3.2 PROBABILISTIC SEISMIC HAZARD ANALYSIS RESULTS ................... 7 4.0 CONCLUSIONS ............................................................. 9 5.0 REFERENCES ............................................................. 10 APPENDIX A INDEPENDENT SEISMIC HAZARD EVALUATION BY Dr. NORMAN A. ABRAHAMSON i 1.0 INTRODUCTION This document provides a summary discussion on seismicity and expected site accelerations due to future earthquakes at Elsmere Canyon proposed to be used as a landfill site by Elsmere Corporation (a subsidiary ofBKK Corporation). Elsmere Canyon is located south and east of the City of Santa Clarita, approximately 0.5 mile northeast of the existing State Route 14/Interstate 5 (SR/1-5) interchange. The site is located in a highly active seismic area. The Los Angeles metropolitan area and particularly San Fernando Valley where the landfill project is proposed to be located, is geologically very complex, with numerous active faults beneath the area. Moderate or large earthquakes (magnitude 6.5 to 7.5) on these faults could potentially cause even more damage than a much larger earthquake on the more distant and notable San Andreas fault. This was dramatically demonstrated by the 1994 magnitude 6.7 Northridge earthquake, the second most expensive natural disaster in the U.S. history (after Hurricane Andrew). More than 100 active faults have been identified in the Los Angeles region. Some of these are hidden blind thrust faults which were discovered only recently after the 1987 Whittier and the 1994 Northridge earthquakes. Three of the most hazardous faults, capable of generating earthquakes with maximum magnitudes in the range of 7 to 7.5, are located only less than 5 miles from the site. One of these, the San Fernando -Sierra Madre -Cucamonga fault zone which is about 5 miles from the site, with a fault plane dipping under the Elsmere Canyon, is capable of generating a large earthquake with a magnitude as high as 7.4. The rupture mechanism for this fault is similar to what occurred on the fault which was the source of the Northridge earthquake. The magnitude 6.7 Northridge earthquake surprisingly generated very high accelerations for a large distance from the earthquake. epicenter. Therefore, it is expected that a big earthquake (magnitude higher than 7) on any of the three major faults located only less than 5 miles from the site (Santa Susana fault zone, San Gabriel fault, and San Fernando -Sierra Madre -Cucamonga fault zone) can generate extremely intense shaking at the Elsmere Canyon. According to a recent study by the scientists of the Southern California Earthquake Center at University of Southern California (Dolan et al., 1995), there is a high probability of occurrence of large (magnitude 7.2 to 7.5) earthquakes in the Los Angeles metropolitan area about every 140 years. 1.1 REGULATORY REQUIREMENTS The primary geologic and seismic regulatory requirements for seismic design of municipal solid waste landfill facilities (MSWLF) are contained in the California Code of Regulations (CCR) Title 23, Chapter 15, and Title 14, Chapter 3, and Title 40 Code of Federal Regulations. (CFR), Subtitle D, Part 258, § 258.14 of the Resource Conservation and Recovery Act (§ 258:14 of Subtitle D). Federal regulations which provide more stringent design requirements specify that new or expansion of existing MSWLF units be "designed to resist the maximum horizontal acceleration (MM) in lithified earth material." The MHA is defined as "the maximum horizontal acceleration depicted on a seismic hazard map with a 90 percent or greater probability that the acceleration will not be exceeded in 250 years, or the maximum expected horizontal acceleration based upon a site-specific seismic risk assessment." The MHA can be also defined as the horizontal peak ground acceleration (PGA) in lithified earth material with a probability of exceedance of 10 percent in 250 years. This exceedance level probability is equal to an average return period of 2,370 years or roughly equivalent to 2,400 years. It is important to note that the Subtitle D regulations for design of landfills are "self -implementing." The current version of map sheet MF -2120, the USGS seismic hazard maps for the continental United States, indicates that the MHA for the Elsmere Canyon is greater than 0.8g. Based on the recent ongoing reassessment of seismicity of the area initiated after the Northridge earthquake (e.g., Dolan et at., 1995), the USGS seismic hazard map underestimates seismic activity and potential earthquake hazards, particularly extent of the shaking intensity, at the site during future earthquakes. Thus, according to the Federal Regulations (§'258.14 Subtitle D), a site-specific seismic risk analysis was performed to estimate site accelerations (MHA). The present report addresses the following issues: 1) The potential regional and local seismogenic sources and thew influence on the site. 2) Regional historic seismicity in an area around the site sufficiently large to include major sources of seismic activity capable of generating ground accelerations of engineering interest at the site. 3) Site specific seismic risk analysis to evaluate site accelerations according to the state and federal seismic design codes and regulations for Class III (MSI) landfills. 2 2.0 FAULTING AND SEISMICITY 2.1 GENERAL This section presents and discusses the available data on active faulting and seismicity within a specified radius of 100 kilometers (approximately 60 miles) from Elsmere Canyon, and describes the procedures used to arrive at the site design peak ground acceleration (PGA). A large number of data sources, particularly recent publications on faulting and seismic activity in Los Angeles and Ventura basins, including published data after the January 17, 1994 Northridge earthquake, were used to provide the required information on faulting and seismicity in the site region. These sources are listed in Section 5.0 of this report. A probabilistic seismic hazard analysis was performed to determine the site-specific PGA for the 2,400 -year return period ground motions as required by Subtitle D. Additionally, as part of this study, an independent site-specific seismic hazard analysis by Dr. Norman A. Abrahamson (Appendix A), was also performed to evaluatelverify results of the analyses presented in the main text of the report. 2.2 TECTONIC SETTING Elsmere Canyon lies near the western end of the San Gabriel Mountains, an east -west trending range within the western Transeverse Ranges Geomorphic Province (Transverse Ranges Province) of California. The Transverse Ranges Province is an east -west trending region consisting of numerous east -west trending mountain ranges and associated basins or valleys. Elsmere Canyon proper begins near State Route (SR) 14, where it joins Whitney Canyon to form Newhall Creek. From SR 14, Elsmere Canyon can be traced to the southeast approximately one and one-quarter miles where it divides into a northern and a southern branch, referred to as Elsmere Canyon North and South (Dames & Moore, 1995). Whitney Ridge, which ranges in elevation from approximately 1,800 feet to 2,700 feet above mean sea level, bounds Elsmere Canyon to the north and northwest. An unnamed ridge, which ranges in elevation from approximately 2,350 feet to greater than 3,200 feet above mean sea level, forms the southwestern, southern, and eastern boundaries of the project property. The Transverse Ranges Province is tectonically controlled by a series of generally north dipping reverse or thrust faults. These faults strike primarily east -west or east-northeast, sometimes with a component of left lateral slip and slip rates in the submillimeter to several millimeter ranges. The Transverse and Peninsular Ranges Provinces merge in the vicinity of the Los Angeles region as documented by the earthquake activity in the greater Los Angeles area since 1987. Major active faults associated with the Transverse Ranges Province include: Santa Monica -Hollywood, Santa Susana, Sierra Madre (San Fernando, Raymond, Cucamonga), and newly discovered faults associated with deeply buried, shallow dipping "blind thrusts" which underlie a major portion of the Los Angeles Basin. Tectonic stresses transferred across the Transverse Ranges Province as a consequence of north -south compression on the San Andreas Fault, have resulted in the rupture of deeply buried blind thrust faults within 3 the Los Angeles region. The October 1, 1987, M5.9 Whittier Narrows Earthquake occurred along the Elysian Park Blind Thrust Fault which is part of the blind thrust system. The recent M6.7 Northridge Earthquake of January 17, 1994, is also believed to be associated with the blind thrust system (Davis & Namson, 1994; Yeats & Huftile, 1995). The features are described as "blind thrust" primarily because their fault planes do not project to the ground surface. The. current model suggests that there may be many similar features underlying large portions of the basins and adjacent uplands within the Transverse Ranges Province. The style of faulting appears to be a result of the merging of two dissimilar structural regimes associated with the Transverse Ranges Province and the northwest -trending San Andreas Fault System. 2.3 FAULTING AND SEISIVIICITY 2.3.1 FAULTING Regional and local geologic and fault studies conducted by the California Division of Mines and Geology (CDMG) (Petersen et al., 1996; Jennings, 1994; Kahl, 1985 and 1986), U.S. Geological Survey (USGS) (Ziony and Jones, 1989; Ziony, 1985), and Southern California Earthquake Center (SCEC) (Jackson et al., 1995; Dolan et al., 1995) were used to delineate and characterize faults in proximity to Elsmere Canyon. Major faults that have been identified as active or potentially active by the CDMG (Jennings, 1994) within a 100 -km radius of Elsmere, and may influence the site with regard to earthquake activity (ground motions), are shown in Table 1. The table provides information on the fault to site distance and direction; fault length, dip angle, and slip rate; type of the fault (sense of movement); and Maximum Credible Earthquake (MCE) associated with each fault. Maximum credible moment magnitudes (Mw) were obtained from several recent publications on faulting and seismicity of southern California (see Table 1). When maximum credible magnitudes were not available from these sources, they were estimated from the surface rupture length and rupture area versus moment magnitude relationships developed by Wells and Coppersmith (1994), using fault lengths estimated from Ziony and Jones (1989). The fault dip angles and slip rates were mainly derived from the SCEC (Jackson et al., 1995 and Dolan et al., 1995) and the CDMG (Petersen et al., 1996) models of the southern California seismicity. Several other sources were also used in estimating the fault parameters for the probabilistic seismic hazard analyses presented later in this report (see Table 1). Figure 1 shows the locations of the active and potentially active faults, and historical earthquake epicenters within a 100 -km radius of the Elsmere Canyon site. Seismic activity within 100 km of the site appears to occur in four general regions with the exception of random events. One of the more seismically active area;, within the 100 -km radius, is near the confluence of the Pletto and White Wolf Faults (approximately 85 km northwest of the site). A second seismically active area encompassing the site is identified near the confluence of the Santa Susana, Sierra Madre, and Verdugo Faults (approximately 5 to 10 km south- southeast of the site). This active zone also trends slightly to the northeast and encompasses a portion of the San Gabriel Fault Zone. The other two seismically active areas are less pronounced than the preceding two, and consist of: the central Los Angeles Basin area including the zone along the Newport -Inglewood Fault about 50 to 80 km southeast of the site; and an area along the eastern portion of San Fernando -Sierra Madre - Cucamonga Fault Zone, approximately 85 km east-southeast of the site. Elsmere Canyon is surrounded by three major faults less than 4 miles from the site. These are the Santa Susana and San Gabriel faults and the Sierra Madre Thrust fault zone (San Fernando, Dunsmore, Sierra 0 Madre, Duarte, Claremont, and Cucamonga segments). The trace of the 1971 San Fernando Earthquake fault rupture is also located less than a mile to the south of the site. Based on the activity rates, and proximity to the site, these faults provide the highest influence on the probabilistic hazard at the site. The other local and regional faults with a significant effect on the site probabilistic hazard are the San Cayetano, Simi -Santa Rosa, Oak Ridge, Holser, and the San Andreas Fault. There are many additional faults within 100 km of the site; however, the probabilistic hazard will be dominated by these faults. Appendix A provides brief descriptions of the major faults influencing the site seismic activity. 2.3.2 SEISMICITY An earthquake computer search (Blake, 1993, 1995) was performed to list and graphically show where historic earthquakes (epicenters) have occurred relative to the proposed Elsmere Canyon landfill site. The computer search was confirmed by cross referencing with another source (Stover and Coffman, 1993). The epicenters are shown on Figure 1. A search was made within a radius of 100 km from the center of the site. Figure 1 also shows the location and coordinates of the site. Earthquakes with a local magnitude 4.0 and larger that have occurred since 1800 are shown in Figure 1. The search produced more than 600 events, with the largest recorded event being the Mw 7.5 (Ms 7.7) 21 July 1952 Kern County earthquake, located about 87 km northwest of the site. The closest moderate sized earthquake (the Mw 6.6 February 9, 1971 San Fernando earthquake) was located about 10 km northeast of the site on the San Fernando fault. Seven earthquakes ranging between ML4.4 to ML6.4 have occurred in the greater Los Angeles Basin from 1987 to 1994. At least five faults have been active in this sequence. The October 1, 1987, Whittier Narrows and June 12, 1988, Montebello events occurred on the Elysian Park Blind Thrust. The December 3, 1988 Pasadena earthquake was a result of left lateral movement on the Raymond fault and the two Upland events (June 26, 1988 and February 28, 1990) were associated with a similar type of displacement along the San Jose fault. The June 28, 1991 Sierra Madre fault event is believed to have occurred on the Clamshell-Sawpit splay with dominantly thrust movement. The January 17, 1994, Northridge earthquake is believed to have occurred on a previously unknown blind thrust fault. None of the earthquakes caused surface rupture and hypocenter depths were in excess of 9 km. The earthquakes discussed above were all associated with crustal fault adjustment within the Transverse Ranges and are within 80 km of the site. Significant recent events in southern California located at a distance greater than 100 km from the site were the June 28, 1992 Landers (Mw 7.3) and Big Bear (Mw6.2) earthquakes (Jackson et at., 1995). These events were associated with strike -slip movement on northwest trending faults east of the San Andreas fault. 3.0 PROBABILISTIC SEISNUC HAZARD EVALUATION A probabilistic seismic hazard evaluation was performed to evaluate the PGA with an average 2,400 -year return period (design ground motion used in Subtitle D). The site is located at 118.490'W and 34.352"N, in San Fernando Valley, California (Figure 1). 3.1 APPROACH A current approach used in seismic hazard evaluation is to develop a probabilistic source model based upon the regional structural geology, tectonics, and historical seismicity (Comell, 1968). The results of this study are usually presented in the form of a plot of horizontal peak ground acceleration (PGA) versus annual frequency of exceedance or average return period. The necessary input for a seismic hazard evaluation consists of. (1) a source model, (2) the seismic activity and frequency -magnitude relationship, and (3) the attenuation relationship between maximum horizontal ground acceleration, earthquake magnitude, and source -site distance. The probabilistic seismic risk analysis was performed using the computer code EZ -FRISK' (Risk Engineering, Inc., 1995). The program models earthquake sources as both lines (faults) and area sources (appropriate when the causative faults are unknown), and calculates annual frequencies of exceedance of various ground motion levels at the site due to the sources within a specified area around the site. In the analysis of the seismic risk at Elsmere Canyon, the analysis area around the site was selected to be a 100 - kilometer -radius circle. Effects of three-dimensional geometry of faults are also modeled in the program by fault trace coordinates, dip angle varying with depth, and fault depth data providing information on location, length, strike, dip, and width of the faults. Modeling the three-dimensional planar geometry of faults is particularly critical for reliable evaluation of the impact of the near -field faults on the site design ground motions. Regional faults within 100 km of the project site were modeled, depending on their distance from the site, as linear or planar sources in this seismic hazard evaluation. Effects of unknown seismic sources such as blind thrust faults and random seismicity on the site ground motions were also considered by an area source encompassing the site. Based on the activity rates, and proximity to the site, the faults that will have a significant effect on the probabilistic hazard at the site are the Santa Susana, San Gabriel, Sierra Madre Thrust fault zone (San Fernando, Dunsmore, Sierra Madre, Duarte, Claremont, and Cucamonga segments), Oak Ridge, San Cayetano, Simi -Santa Rosa, and the San Andreas fault. There are many additional faults within 100 km of the site; however, the probabilistic hazard will be dominated by these faults. The magnitude recurrence relation depends on the slip -rate, maximum magnitude, minimum magnitude, and magnitude distribution (relative number of small and large earthquakes). The earthquake occurrence is assumed to follow a Poisson model (no memory), but two alternative magnitude density functions are considered. The recurrence curve representing the frequency of occurrence of earthquakes of various sizes (magnitudes) for a seismic source was modeled using either the truncated exponential model or the characteristic -magnitude model. Except for the area source and few faults that the truncated exponential model was used, the characteristic model proposed by Youngs and Coppersmith (1985) was used in this 0 seismic hazard evaluation. The characteristic model assumes that more of the seismic energy is released in large magnitude events than for the truncated exponential model. That is, there are fewer small magnitude events for every large magnitude event for the characteristic model than for the truncated exponential model. Recent studies have found that the characteristic model does a better job of matching observed seismicity than the truncated exponential model (Geomatrix, 1992). The basic inputs for the probabilistic analyses using the above program are: • Site coordinates. • Rupture mechanism and geometry of the seismic sources and their location with respect to the site (the source mechanism such as strike slip, reverse, normal, or oblique; fault trace coordinates, dip angle, and depth information). • Recurrence curve information specifying the average number of earthquakes per year of given magnitudes occurring within the seismic sources. This information includes fault slip rate, total annual rate of occurrence of earthquakes exceeding a minimum magnitude in the truncated exponential model, b -value [the slope of the best -fit line from a Gutenberg -Richter (1954) recurrence plot], and parameters of the characteristic -magnitude model. • Maximum magnitudes associated with the faults and area sources. • Parameters of the rupture -length equation. • Attenuation relationships. Faults in close proximity of the site were digitized in detail from the 1:24,000 scale Earthquake Fault Zones maps (formerly Special Study Zones maps) of the State of California prepared by the California Division of Mmes and Geology (CDMG) in compliance with "Alquist-Priolo Earthquake Fault Zoning Act." The rest of the faults in the analysis area, were digitized from the CDMG, 1:750,000 scale fault activity map of California (Jennings, 1994). The information regarding fault slip rates, b -values, maximum magnitudes, dip angles, depths, source mechanism, appropriate recurrence, fault rupture, and attenuation relationships were derived from some of the most recent publications on seismic activity and faulting in Southern California (Petersen et al., 1996; Jackson et al., 1995; Dolan et al., 1995; Wells and Coppersmith, 1994; Boore et al., 1993 and 1994; Sadigh et al., 1993 and 1994; Idriss, 1993; Wesnousky, 1986; Ziony and Yerkes, 1985). 3.2 PROBABILISTIC SEISMIC HAZARD ANALYSIS RESULTS The results of the probabilistic analyses for the site design Peak Ground Acceleration (PGA) are presented in Figures 2 through 5. Figures 2 and 3 illustrate annual rates of exceedance and average return period of the PGA at the site for different acceleration values, respectively. These figures present results of a probabilistic seismic hazard analysis of the site mainly based on the SCEC's seismic source model (source parameters for critical faults influencing the site seismicity were derived from Dolan et al., 1995 and Jackson et al., 1995, see Table 1). Figures 4 and 5 present similar results for the seismic hazard analysis of the site based on the CDMG's seismic source model (source parameters for critical faults influencing the site seismicity were estimated from Petersen et al., 1996). The attenuation relationship of Idriss (1993) for the PGA, which was developed based on recorded accelerations at bedrock and stiff soil sites, was considered suitable for the proposed landfill site which is underlain by rock. The analysis was also performed using two other recent attenuation equations; also developed for firm ground sites, to verify the possible range of the 7 PGA at the site. These equations were: Q) Boore-Joyner-Fumal (1994) for site "class B" and (2) Sadigh, et al. (1994) for rock. As indicated from the E6,ures, the three attenuation relations provide comparable PGA estimates for the 2400 -year -return -period event (the Subtitle D design earthquake). The PGA, estimated using the Idriss (1993) equation, is approximately equal to the average of the values estimated from the other two attenuation relations. As shown in Figures 3 and 5, the mean values of the PGA (average of the results from the three attenuation relations) for the 2400-year-retum-period earthquake are estimated at 1.2g to 1.3g for the Elsmere Canyon site. Appendix A presents results of another seismic hazard analysis for the Elsmere Canyon site conducted independently by Dr. Norman A. Abrahamson as part of this study. The results of this independent analysis show a peak acceleration of 1.13g for the ground motion with approximately 2400 -year return period (Subtitle D design motion). 4.0 CONCLUSIONS The US Code of Federal Regulation (USEPA Subtitle D) requires that all landfills within a "seismic impact zone" be "designed to resist the maximum horizontal acceleration in lithified earth material" (MITA). The MHA is defined as "the maximum horizontal acceleration depicted on a seismic hazard map with a 90 percent or greater probability that acceleration will not be exceeded in 250 years, or the maximum expected horizontal acceleration based upon a site-specific seismic risk assessment." This corresponds approximately to the acceleration generated by the 2400 -year return period earthquake. A "seismic impact zone" is defined as a region within which the maximum horizontal acceleration for the stated probability level is greater than 0.1g. The USGS seismic hazard Map Sheet MF72120 shows the approximate levels of acceleration to be considered for design of landfills across the United States. From this map, it can be observed that the proposed Elsmere Canyon landfill is located in a seismic impact zone and should be designed for a maximum horizontal acceleration greater than 0.8g. In the present study, a site-specific seismic hazard analysis of the proposed Elsmere Canyon landfill was conducted to evaluate a more reliable estimate of the site MHA for the approximately 2400 -year return period earthquake, as required by USEPA Subtitle D regulations for seismic design of landfills. The postulated Subtitle D design earthquake for the proposed Elsmere Canyon landfill was characterized by a peak horizontal acceleration in lithified earth material of approximately 1.2g to 1.3g. A second independent seismic hazard analysis of the site (Appendix A) resulted in a maximum horizontal site acceleration of 1.13g, verifying the peak acceleration computed here for the Subtitle D design ground motion. Therefore, according to the results of the site-specific seismic hazard analysis presented in this report, the proposed Elsmere Canyon landfill should be designed for an MHA level exceeding 1.Og in order to satisfy federal regulations for seismic design of municipal solid waste landfills. The Draft Environmental Impact Report/Draft Environmental Impact Statement (DEIR/DEIS) prepared for the proposed Elsmere Canyon landfill (Dames and Moore, 1995) does not adequately evaluate the seismic impacts, particularly the potential for severe seismic -induced ground shaking, on the project. The DEIR/DEIS document fails to recognize the need for an up-to-date seismic hazard analysis of the site which includes the most recent information on the seismicity, seismic source model, and ground motion attenuation relations developed for the region after the recent seismic events in southern California, particularly the January 1994 Northridge earthquake. The preliminary site acceleration of 0.6g estimated in the DEIR/DEIS is too low and provides a nonconservative measure of the shaking intensity compared with the site acceleration (--1.2g) estimated for the 2400 -year return period earthquake in the present site-specific seismic hazard study. 5.0 REFERENCES Blake, T. F. (1993), "EQSEARCH Computer Program," Thomas F. Blake Computer Services and Software. Blake, T. F. (1995), Annual Update of California Seismicity Data Base, Thomas F. Blake Computer Services and Software. Boore, D. M., W. B. Joyner, and.T. E. Fumal (1993), "Estimation of Response Spectra and Peak Accelerations from Western North American Earthquakes," An Interim Report, U.S. Geological Survey Open -File Report 93-509, 72 pp. Boore, D. M., W. B. Joyner, and T. E. Fumal (1994a), "Estimation of Response Spectra and Peak Accelerations from Western North American Earthquakes," An Interim Report, Part 2, U.S. Geological Survey Open -File Report 94-127,40 pp. Boore, D. M., W. B. Joyner, and T. E. Fumal (1994b), "Ground Motion Estimates for Strike- and Reverse - Slip Faults," U.S. Geological Survey, Unpublished Note. Comell, C. A. (1968), "Engineering Seismic Risk Analysis," Bulletin of Seismological Society of America, Vol. 58, No. 5, pp. 1583-1606, October. Dames & Moore (1995), "Draft Environmental Impact Report/Enviromnental Impact Statement - Proposed Elsmere Solid Waste Management Facility," prepared for U.S. Department of Agriculture, Forest Service and Los Angeles County Department of Regional Planning, January. Davis, T. L. and J. S. Namson (1994), "A Balanced Cross -Section of the 1994 Northridge Earthquake, Southern California," Nature 372, 167-169. Dolan, J. F., K. Sieh, T. K. Rockwell, R. S. Yeats, J. Shaw, J. Suppe, G. J. Huftile, and E. M. Gath (1995), "Prospects for Larger or More Frequent Earthquakes in the Los Angeles Metropolitan Region," Science, Vol. 267, January 13, 199-205. Geomatrix (1992), "Seismic Ground Motion Study for the West San Francisco Bay Bridge," Report to Caltrans, Contract No. 59N772. Gutenberg, B. and C. F. Richter (1954), "Seismicity of the Earth," Princeton University Press, 310 pp. Idriss, I. M. (1993), "Procedures for Selecting Earthquake Ground Motions at Rock Sites;" National Institute of Standards and Technology, NIST GCR 93-625, 7 pp. Jackson, D. D., K. AkL A. A. Cornell, J. H. Dieterich, T. L. Henyey, M. Mandyiar, D. Schwartz, and S. N. Ward (Southern California Earthquake Center - SCEC 1995), "Seismic Hazards in Southern California: Probable Earthquakes, 1994-2024," BSSA, Vol. 85. 10 Jennings, C. W. (1994), "Fault Activity Map of California and Adjacent Areas," California Department of Conservation, Division of Mines and Geology, Geologic Data Map No. 6, Scale 1:750,000. Jones, L. M. and E. Hauksson (1994), "Review of Potential Earthquake Sources in Southern California," Proceedings of Seminar of New Developments in Earthquake Ground Motion Estimation and Implications for Engineering Design Practice, ATC 35-1, January 26. Kahle, J. E. (1985), "The San Cayetano Fault near Fillmore, the Lion Fault in Upper Ojai Valley, and the Arroyo-Patrida-Santa Ana Fault near Mira Monte, Ventura County, California," California Division of Mmes and Geology Fault Evaluation Report, FER-174, 25 p. Kahle, J. E. (1986); "The San Gabriel Fault near Castaic and Saugus, Los Angeles County, California," California Division of Mmes and Geology Fault Evaluation Report, FER-178. Petersen, M. D., C. H. Cramer, W. A. Bryant, M. S. Reichle, and T. R. Toppozada (1996), "Preliminary Seismic Hazard Assessment for Los Angeles, Ventura, and Orange Counties, California Affected by the January 17, 1994 Northridge Earthquake," Bulletin of Seismological Society of America, Vol. 85, No. 6, February. Risk Engineering, Inc. (1995), "EZ -FRISK'"{ User's Manual, Version 2.0," Boulder, Colorado. Sadigh, K, C. Y. Chang, N. A. Abrahamson, S. J. Chiou, and M. S. Power (1993), "Specification of Long - Period Ground Motions: Updated Attenuation Relationships for Rock Site Conditions and Adjustment Factors for Near -Fault Effects," in Proceedings of ATC -17-1 Seminar on Seismic Isolation, Passive Energy Dissipation and Active Control, Applied Technology Council, Redwood City, California, Vol. 2, pp 59-70. Sadigh, K. and others (1994), Written communication to the Southern California Earthquake Center, Los Angeles, Calif., by Geomatrix Consultants, San Francisco, Calif. Stover, C. and J. Coffman (1993), "Seismicity of the United States, 1568-1989," U.S. Geological Survey Professional Paper 1527. Wells, D. L. and K. J. Coppersmith (1994), "New Empirical Relationships Among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement;" Bulletin of Seismological Society of America, Vol. 84, 974-1002. Wesnousky, S. G. (1986), "Earthquakes, Quaternary Faults, and Seismic Hazards in California," Journal of Geophysics Research, Vol. 91, 12587-12631. Yeats, R. S. and G. J. Huflile (1995), "Oak Ridge Fault System and the 1994 Northridge, California Earthquake," Nature 373, 418-420. Yerkes, R. F. (1985), "Geologic and Seismologic Setting," in J. I. Ziony (Editor), Evaluating Earthquake hazards in the Los Angeles Region—An Earth -Science Perspective, U.S. Geological Survey Professional Paper 1360, 25-43. 11 Youngs, R. R and K. J. Coppersmith (1985), "Implications of Fault Slip Rates and Earthquake Recurrence Models to Probabilistic Seismic Hazard Estimates," Bulletin of Seismological Society of America, Vol. 75, pp. 939-964. Ziony, J. I. (Editor), "Evaluating Earthquake hazards in the Los Angeles Region --An Earth -Science Perspective," U.S. Geological Survey Professional Paper 1360,43-91, 1985. Ziony, J. I. and L. M. Jones (1989), "Map Showing Late Quaternary Faults and 1978-84 Seismicity of the Los Angeles Region, California," U.S. Geological Survey Miscellaneous Field Studies Map MF -1964, Scale 1:250,000. Ziony, J. I. and R. F. Yerkes (1985), "Evaluating earthquake and Surface Faulting Potential," in J.1. Ziony (Editor), Evaluating Earthquake hazards in the Los Angeles Region—An Earth -Science Perspective, U.S. Geological Survey Professional Paper 1360, 43-91. 12 TABLE 1 MAJOR FAULTS WITHIN A 100 -KILOMETER RADIUS OF THE ELSMERE CANYON SITE FAULT APPROXIMATE DISTANCE AND DIRECTION FROM Srrgc FAULT LENGTH`' (km) FAULT DIPm SLIP RATEot (mm/yr) TYPE OF FAULT (SENSE OF SLIP)un MAGNITUDE (Ma.) OF MAXIMUM CREDIBLE EARTHQUAKE(' AGE AND EVIDENCE OF LATEST SURFACE FAULTINGi' Santa Susem 3AS 30 60' N 55' 6.0(3.0) Reverse 6.9(6.7) Late Quaternary Sen Gabriel 3.8N 100 60• N 0' 1.0 Strike Slip 7.0 .1 Holocene mar Castaic- LateQ"wmary Siem Madre -San Fernando 7ASE 85 600 N 45• 4.0 .0 Reverse 7.3(7.2) Holocene and Late Quaternary Verdu o -Ea Ie Rock 12.8SE 27 45' - 60' NE 0.1 Reverse Oblique 6.4 Holocene Northridge Hills 12.9S 20 35' - 80' N 0.5 Reverse Oblique 6.7 Late atema • Historic Holser 15ANW 19 650 S 0.6 Reverse 6.3 Late Quaternary Simi -Santa Ron 17ASW 36 60' N 0.9 Reverse Oblique 6.9(6.9)- Late Quaternary Oak Ride Onshore 22.3W 42 1 50' S 65' S 4.9 Reverse Oblique 7.3(7.5) Late terns • Holocene near Fillmme Cleawater 26AN 30 80' N 0.05 Normal Oblique 6.9 Late Quaternary San Ca etano 28.5W 50 45• N 60' 6.0 Reverse 7.0 Holocene Santa Monica -Hollywood 31 ASSE 5o 65• - 70' N 1.5 Reverse Oblique 7.0 Late Ouaternary Ne rt -In lewood 33.9SE 95 74' NE - 90' 1.0(1.5) Strike Slip 7.0 Holocene onh Branch • LateQ"temary EI aian Park Seismic Zone 34.25E 41 22' NE 1.7 Blind Thorn -Reverse 7.0 Historical 1987 Whinier Narrows Event San Andreas o ave 34.7N 337 90' 34.0 Strike Slip 8.0 Historical 185 SE to Wrihtwood Raymond 35.5SE 22 80' NE 0.4 Reverse Oblique 6.7 Historical 1988 M4.9 Pandena Earthquake) Malibu Coon 37.OSW 1 50 75' N 1.5 Reverse Oblique 6.9 Late aterna• Holocene (1) Petersen et A., 1996; Jackson et al., 1995; Blake, 1993; Jennings, 1994; Ziony and Jones, 1989; Weanousky, 1986; Ziony and Yerkes, 1985. Refinements were made to fault traces for mar -field faults using state of California Special Studies Zone pupa. (2) Petersen et al., 1996; Dolan et al., 1995; Yerkes, 1985; Wesnouaky, 1986; Ziony and Yerkes, 1985. (3) Petersen et al., 1996; Dolan at al., 1995; Jackson et al., 1995; Wesnousky, 1986. (4) Petersen et al., 1996; Dolan et al., 1995; Wesnounky, 1986; Ziony and Yerkes, 1985. (5) Petersen et al., 1996; Jackson et al., 1995; Dolan et al., 1995; Wenwusky, 1986. When maximum erodible moment magnitudes for faults were not available from these sources, they were estimated from the surface rupture length and rupture arm versa moment magnitude relationships developed by Wells No Coppersmith (094). (6) Jackson et al., 1995; Ziony and Yerkes, 1985. TABLE 1 MAJOR FAULTS WITHIN A 100 -KILOMETER RADIUS OF THE ELSMERE CANYON SITE (Continued) FAULT APPROXIMATE DISTANCE AND DIRECTION FROM SrrEt" FAULT LENGTH"' 0—) FAULT DIPM SLIP RATE"' (mm)yr) TYPE OF FAULT (SENSE OF SLIP))- MAGNITUDE (Ma.) OF MAXIMUM CREDIBLE EARTHQUAKE'^ AGE AND EVIDENCE OF LATEST SURFACE FAULTING" Whinier -North Elrinore 38.7SE 70 70' NE 5.0 Strike Slip 7.5 Late Quaternary NW of Brea Canyon Pine Mountain 40ANW 60 9o' 0.1 Reverse 7.0 Late Quaternary Santa Ynez et 45.1NW 90 90' 1.0 Strike Slip 7.5 Late Ouaternary Palos Verdes 45.35 -SE 106 70' SW 3.5 Reverse Obki ue 7.2 Holocene in San Pedro Ba Annea a 51.7SW 86 45' N 1.0 Reverse 7.2 Holocene Arroyo Parids 59.7W so 70' N 0.4 Reverse 7.3 Late Quaternary (1) Petersen et al., 1996; Jackson et al., 1995; Blake, 1993; Jennings, 1994; Ziony and Jones, 1989; Wewou.ky, 1986; Ziooy and Yerkes, 1985. Refinements were made to fault traces for near -field faults using state of California Special Studies Zone maps. " (2) Petersen et A., 1996; Dolan el al., 1995; Yerkes, 1985; Wesnousky, 1986; Ziony and Yerkes, 1985. (3) Petersen et al., 1996; Dolan et al., 1995; Jackson el al., 1995; Wesnousky, 1986. (4) Petersen et al., 1996; Dolan at al., 1995; Wesnousky, 1986; tinny and Yerkes, 1985. - (5) Petersen et al., 1996; Jackson U al., 1995; Dolan at al., 1995; Wese ousky,'1986. When maximum credible moment magnitudes for faults were not available from these sources, they were estimated from the surface rupture length and rupture area versus moment magnitude relationships developed by Wells and Coppersmith (1994). (6) Jackson et al., 1995; Ziony and Yerkes, 1985. NOTE: The information on fault trace coordinates, dip angles and slip rates, magnitude of fault maximum credible earthquake, and fault types were used in the probabilistic evaluation of the site seismic design parameters. Fault dip angle and its maximum credible earthquake magnitude were estimated from the range of values provided in the above referenced literature. Two separate probabilisitie seismic hazed analyses using different fault dip, slip rete, and maximum magnitude values for faults with the highest influence on the site seismicity were performed. In the fust analysis the fault parameters were selected mainly from the Southern California Earthquake Center seismicity model for southern California (Jackson et al., 1995; Dolan et al., 1995), while in the second analysis some of the fault parameters for several faults were changed based on the latest CDMG model for the southern California seismicity (Petersen et al., 1996). The fault parameters used in the second seismic hazard evaluation for the site are shown in parentheses. .i 1 SIERRA NEVADA - FAULT � 7Y► , i I i ' • • • JV v ? SRO • •��_ •• to Q C fr PJryF MFANr I.., T iFAUtc9BR�C'FA `T FR� f FpuLs SITE Q -Z j ANACAPA FAULT ASN j� \ (>S• Al \ t AUBU COAST • ` \ , FAULT .. \ I • D� r 1 , .�, i��__ �� •moi C i C I DC I I j 1 „ •I Z Z yeIV !Oc "W�afp 9L<r i ___ 135 \ ; AREA COV \ A ti ` I O„ O 25 50 MILES APPSO�XIEMATE i ! AFTER BLAKE EOSEARCH, 1993a 1 EPICENTER REFERENCE: j AFTER BLAKE. 19934; COMO, 1992akb I and 1994: U.S.O.S., 1994 I 1 i (HISTORICAL EARTHQUAKES FROM 1800 TO 1995) I I L�":�"<ey\_ ; LEGEND • r i 0 M = 6.0-6.9 1 <� M = 5.0-5.9 I 9�r M = 4.0-4.9 ?0� P SITE LOCATION: x LATITUDE — 34.352 N LONGITUDE — 118.490 W `\ FIGURE 1 ACTIVE AND POTENTIALLY ACTIVE FAULTS AND HISTORICAL EARTHQUAKE EPICENTERS WITHIN 100 KM OF ELSMERE CANYON ELSMERE CANYON SAN FERNANDO VALLEY, CALIFORNIA am 1 5 2 0.1 5 2 1 E-3 5 2 1 E-4 5 2 1 E-5 0.01 �_■■■■1111■■■■��Attenuation ��■�■■■■111 IIIc Relations .. :.. ' . 9- ■■■��11�■■■ ■■■■1111 �■■■11111��1■■��■i■■�Ili_ :■■ �■■■■1111■�■■1111■■■■1111 I�■■■■1111■■■a►l111�■■■■IIIE !�■■■11111■■■I��al�■■■1111 �■■■■1111■■■■Illi■■■■1111 i�■■■■1111■■■■1111 �■■■■Illi_ �■■■11111■■■11111�`a■■■■111' m■■■■1111m■■■■1111w\■■■■Illi ■■■■1111■■■■1111��■■■�IIIE �■■■11111■■■11111■■■■1111 �■■■■1111■■■■1111■■■■Illi 2 5 0.1 2 5 1 2 .5 10 Acceleration (g) Figure 2. Annual Frequency of Exceedance Versus Acceleration Relationship - SCEC Source Model Proposed Elsmere Canyon Landfill Seismic Hazard Analysis m v 0 a. E a) Of 43) C, CO 100000 5 3 2 10000 5 3 2 WOI� 5 3 2 100 5 3 2 10 5 3 2 1 M■■■■■III�N■■■■111=■■■■■111 Attenuation Relations ldriss - ..(1994) .. ■■■■■111■■■■l11E -_ ■■■■■■11-■■■■■■■� ■■■■1111��■■■■111 ■■■■■111WA■■■■■111 �■■■■1111■■■■1111 �■■■■■■111 �■■■■1111■■■■Ille�■■■■■■IIIE 'i■■■■■111■■■■!1'�il■■■■■■■■111 Imo■■■■■■■��■■■■■�i■�■■■■■■■■■■� ��■■■■1111■■■��111■�■■■■■■111 '�■■■■1111■■■■1111■■■■■■Illi �■■■■■111��'i■■■III■■■■■■■■111 �■■■■1111 ■■■■1111■■■■■■■IIIE �■■�s��■■■■1111■■■■■■IIIE _��®i■111��■■■■III■■■■■■■■111 �■■■■1111■■■■1111■■■■■■Illi 0.01 2 3 5 0.1 2 3 5 1,21 2 3 Acceleration (g) �� 5 10 Figure 3. Average Return Period Versus Acceleration Relationship - SCEC Source Model Proposed Elsmere Canyon Landfill Seismic Hazard Analysis ZO 2 0.1 5 2 1 E-4 5 2 1E-5 0.01 �_■■■■1111■■■■��■■■■111 Attenuation RelationsIlli ��■,11111■■■ 119931SacrIIIA ■■■��I�■■■ldriss 9 ■■■■1111■■:.. ' . :r-Fumal ... 1111 �■■■Illll�i�■I■��■■■■illi I�■■■■1111■®■■1111■■■■1111 ''�■■■■1111■■■�i�lll�■■■■IIIE 'i■■■11111■■■■111��■■■1111 �■■■■1111■■■■111��■■■■1111 �■■■■1111■■■■1111�►`�■■■■Illi �■■■11111■■■11111®►`■■■■111�'� �■■■■1111■■■■1111■►\■■■■IIIE �■■■■1111■■■■1111\■■■■IIIE �■■■11111■■■11111■■■1111 �■■■■1111■■■■1111■■■■Illi 2 5. 0.1 2 5 1 2 5 10 Acceleration (g) Figure 4. Annual Frequency of Exceedance Versus Acceleration Relationship - CDMG Source Model Proposed Elsmere Canyon Landfill Seismic Hazard Analysis LA 100000 5 3 2 ,0000 5 3 2 1000 5 3 2 100 5 3 2 10 5 3 2 ��■■■1111■■■■1111 iAttenuation Relationsldriss 93 ' ' ■■■■■�11�■■■■■SIE ■ee■■■■■eeae■�e■■■■i 1■■■IIII�L■■■■1111 1■■■IIII�I➢■■■■1111 �e■ee■■■■■tee■ee■■■■■■rye■ee■■■■� �■■■■1111■■■■111��,�.■� �■■■■illl�■■■■111, 111E �e�e■■■■■tee■ee■■��■eee■ee■■■■� �■■■■1111■■■��111�■■■■1111 �■■■■1111■■■■1111■■■■Illi_ �e■ele■■■■■� Iele■■■■■�e■ele■■■■E �■■■■1111■■■■1111■■■■IIIE �■■■s�lli�■■■■1111■■■■1111 �_ ��■�■IIIA■■■■■�II�■■■■■�11. ��e■■■■■■tee■ee■■■■■tee■ee■■■■� �■■■■1111■■■■1111■■■■Illil 0.01 2 3 5 0.1 2 3 5 1 2 3 5 10 Acceleration (g) Figure 5. Average Return Period Versus Acceleration Relationship - CDMG Source Model Proposed Elamere Canyon Landfill Seismic Hazard Analysis INDEPENDENT SEISMIC HAZARD EVALUATION SEISMIC HAZARD ANALYSIS FOR THE SITE LOCATED AT 118.490W9 -34.352N (ELSMERE CANYON) A Report Prepared by Dr. Norman A. Abrahamson Engineering Seismology Consultant Norman A. Abrahamson, Ph.D. ENGINEERING SEISMOLOGY CONSULTANT August 24, 1995 Ben Hushmand Hushmand Assoc. 17748 Skypark Circle, Suite 230 Irvine, CA 92714 Dear Ben: I've enclosed the report for the seismic hazard at the site located at 118.490W, 34.352N. Sincerely, ,A`Z, e—, e,- , Norm Abrahamson 5319 Camino Alta Mira Castro Valley. California 94546 Telephone 510.582.9017 Fax 510.582.4025 Ground Motions for the Site at (118.490W, 34.352N) Introduction The site is located in a highly faulted region north of the San Fernando Valley. Based on the activity rates, and proximity to the site, the faults that will have a significant effect on. the probabilistic hazard at the site are the Santa Susana, San Gabriel, San Cayetano, Simi -Santa Rosa, Sierra Madre Thrust fault zone (San Fernando; Dunsmore, Sierra Madre, Duarte, Claremont, and Cucamonga segments), and the San Andreas Fault. There are many additional faults within 100 km of the site, however the probabilistic hazard will be dominated by these faults.. Following Subtitle D, the ground motion with a.90% chance of not being exceeded in 250 years is computed using a site-specific probabilistic seismic hazard analysis. The probabilistic seismic hazard analysis follows the standard approach developed by Cornell (1968). The basic methodology involves computing how often a specified level of ground motion will be exceeded at the site. Subtitle D specifies a ground motion with a 90% chance of not being exceeded in 250 years. Under a Poisson assumption (e.g. no memory of past earthquakes), this corresponds to a return period of 2370 years. The maximum magnitudes, and slip -rates (activity rates) for each fault listed in Table 1 are based on the recent seismic hazard studies by the California Division of Mines and Geology (Petersen, et al.1995) and Wodoward-Clyde,1994. The CDMG model is itself based on the Southern California Earthquake Center model (Working Group on California Earthquake Probabilities, 1995). Brief descriptions of the faults that have a significant contribution to the hazard at the site are given below. Descriptions of Significant Faults Santa Susana Fault The Santa Susana Fault is located approximately 3 km south of the site. The Santa Susana Fault is the closest fault to the site. The Santa Susana Fault has a total length of about 32 km with reverse slip motion dipping to the north (toward the site). There have been no historical earthquakes with magnitude greater or equal to 5.0 associated with the Santa Susana Fault. San Gabriel Fault The San Gabriel Fault is located approximately 4 km north of the site. The San Gabriel Fault has a total length of about 73 km with predominately right -lateral strike -slip motion. There have been no historical earthquakes with magnitude greater or equal to 5.0 associated with the San Gabriel Fault. San Andreas Fault The San Andreas Fault is located approximately 35 km northeast of the site. This section of the San Andreas Fault is called the Mojave Segment. The San Andreas Fault is a predominately right -lateral strike -slip fault extending from Cape Mendocino to Mexico. The northern and southern sections of the fault are divided by the central creeping section south of Hollister to Parkfield. The southern half of the San Andreas Fault is further segmented near San Bernardino at the junction with the San Jacinto Fault. There are four segments of the San Andreas Fault between the creeping section and the San Jacinto Fault junction: Parkfield, Cholame, Carrizo, and Mojave. These four segments may rupture independently or simultaneously. The largest historical earthquake on the Carrizo Plain segment was the 1857, Fort Tejon Earthquake with a moment magnitude of 7.9 (Well and Coppersmith, 1994). This earthquake was due to simultaneous rupture of the Parkfield, Cholame, Carrizo, and Mohave segments. Oakridge Fault The Oakridge Fault is located approximately 34 km west of the site. The Oakridge Fault has a total length of about 97 km with reverse slip motion dipping to the south. There have been no historical earthquakes.with magnitude greater or equal to 5.0 associated with the Oakridge fault. San Cayetano Fault The San Cayetano Fault is located approximately 33 km west of the site. The San Cayetano Fault has a total length of about 45 km with reverse slip motion dipping to the north. There have been no historical earthquakes with magnitude greater or equal to 5.0 associated with the San Cayetano fault. Holser Fault The Holser fault is located approximately 15 km northwest of the site and has a length of 16 km. The motion is predominately reverse with the fault dipping approximately 45 degrees to the north. There have been no historical earthquakes with magnitude greater or equal to 5.0 associated with the Holser fault. Simi -Santa Rose Fault The Simi -Santa Rosa Fault is located approximately 17 km southwest of the site. The Simi -Santa Rosa fault system has a total length of about 36 km with reverse slip motion dipping to the north. There have been no historical earthquakes with magnitude greater or equal to 5.0 associated with the Simi -Santa Rosa fault system. Sierra Madre Thrust Zone The Sierra Madre.Thrust zone consists of several east -west trending thrust faults: San Fernando Fault, Dunsmore Fault, Sierra Madre Fault, Duarte Fault, Claremont Fault, and Cucamonga Fault. The site is located closest to the San Fernando segment which is about 6 km to the southeast. The total fault length of the Sierra Madre Thrust zone is about 63 km. The San Fernando segment has a length of 20 km. The largest historical earthquake on the Sierra Madre Thrust zone was the 1971 San Fernando earthquake with magnitude 6.6. This event ruptured the San Fernando segment of this fault system. Probabilistic Hazard Calculation The probabilistic seismic hazard analysis follows the standard approach developed by Cornell (1968). The basic methodology involves computing how often a specified level of ground motion will be exceeded at the site. The hazard analysis computes the annual number of events that produce a ground motion parameter, Z, that exceeds a specified level, z. This number of events per year, v, is also called the "annual frequency of exceedance". The inverse of v is called the "return period" and is given in years. Once this annual frequency of occurrence is obtained, the probability of this level of ground motion being exceeded over a specified time period is computed using the following expression: P = 1- exp(-vt) (1) where P is the probability of this level of ground motion being exceeded in t years. This calculation assumes a Poisson occurrence of earthquakes (that is, there is no memory of past earthquakes). The calculation of the annual frequency of occurrence, v, involves three probability distributions: the frequency of occurrence of earthquakes of various sizes (magnitudes), the location of the earthquakes, and the attenuation of the ground motion from the earthquake rupture to the site. The occurrence rates of the earthquakes of various magnitudes are determined by the magnitude recurrence relations. The location of the earthquake depends on the geometry of the seismic source relative to the site locations. The ground motion at the site is determined from the attenuation relation. The magnitude recurrence relation depends on the slip -rate, maximum magnitude, minimum magnitude, and magnitude distribution (relative number of small and large earthquakes). The location of the earthquakes are determined by randomly locating earthquakes along the fault rupture. The attenuation relation describes the median ground motion for a given magnitude and distance, as well as the variability of the ground motion which accounts for randomness in the ground motions. These parameters are discussed in more detail below. Attenuation Relations Three attenuation relations are used for the hazard analysis. These are the Sadigh et al. (1993), Idriss (1991), and Boore, Joyner, and Fumal (1994) site (class B) attenuation relations for rock For all of the models, the log -normal distribution was truncated at 3.0 sigmas. Recurrence Model There are two parts to the earthquake recurrence model: how many earthquakes occur each year (activity rate) and what is the relative distribution of small and large magnitude events (magnitude density function). The activity rate is computed by balancing the energy build-up from geologic evidence with the total energy release of earthquakes. The geologic evidence is the slip -rate on the fault. Knowing the dimension of the fault, the slip -rate, and the rigidity of the fault, we can balance the long term seismic moment so that the fault is in equilibrium. (Youngs and Coppersmith, 1985). The seismic energy release is balanced by requiring the build up of seismic moment to be equal to the release of seismic moment in earthquakes. The build up of seismic moment is computed from the long term slip -rate. The seismic moment, Mo (in dyne cm), is given by Mo=v AD (2) where µ is the rigidity of the crust, A is the area of the fault (in cm2), and D is the average displacement (slip) on the fault surface (in cm). The annual rate of build up of seismic moment is given by Mo=uAS (3) where S is the slip -rate in cm/year. The seismic moment released during an earthquake is given by log Mo = 1.5 M + 16.05 where M is the moment magnitude of the earthquake. (4) To balance the moment build up and the moment release, the annual moment rate from the slip -rate is set equal to the sum of the moment released in all of the earthquakes that are expected to occur each year. µAS = cJ L f(M)101.5M+16.05 dM ML (5) where f(M) is the probability density function of the magnitude recurrence relation, ML is the minimum magnitude that can cause damage, mU is the maximum magnitude for the seismic source, and c is a constant. The constant c is the only free parameter and it is computed from Equation (5). The earthquake occurrence is assumed to follow a Poison model (no memory), but two alternative magnitude density functions are considered. The magnitude density function describes the relative number of earthquakes at each magnitude. We have considered a truncated exponential model and a characteristic model (Youngs and Coppersmith, 1985). In both cases, a b -value of 0.80 is used for all faults. The characteristic model assumes that more of the seismic energy is released in large magnitude events than for the truncated exponential model. That is, there are fewer small magnitude events for every large magnitude event for the characteristic model than for the truncated exponential model. Recent studies have found that the characteristic model does a better job of matching observed seismicity than the truncated exponential (Geomatrix,1992, Woodward - Clyde, 1994). In the current study, the characteristic model was given 90% weight and the truncated exponential model was given 10% of the weight for all of the faults. Probabilistic Seismic Hazard Analysis Results The peak acceleration hazard is shown in Figures la and lb. The results are presented in terms of the annual probability of exceeding a given level of acceleration (Figure la) and average return period (Figure 1b). For Subtitle D, the ground motion for a 2370 return period is used. This corresponds to an annual probability of exceedance of 0.0042. At this hazard level, the peak acceleration is 1.13g. The hazard curve shows the cumulative effects of the ground motion hazard from various magnitude earthquakes at various distances. For a given level of hazard (e.g. 0.0042 annual probability), the hazard can be broken back down into the contributions from distinct magnitude and distance ranges. This process, called deaggregation, provides additional insight into the dominant sources. The deaggregated PGA hazard for 0.6g is shown in Figure 2. This figure shows that the hazard is dominated by close events (distances of 5-10 km) which corresponds to the earthquakes on the Santa Susana Fault. The mean magnitude (M bar), mean distance (D bar), and mean number of standard deviations (epsilon Bar) from the deaggregated hazard are shown in Figure 3 as a function of the ground motion level. For 1.138, the M bar and D bar correspond to a magnitude 6.6 event at a distance of 4 km. The epsilon bar of 1.8 indicates that this ground motion (1.13g) is on average 1.8 standard deviations above the median level predicted by the attenuation relations. References Boore, D. M., W. B. Joyner, and T. Fumal (1993). Estimation of response spectra and peak accelerations from Western North American earthquakes: an interim report, U.S. Geological Survey, OFR 93-509. Boore, D. M., W. B. Joyner, and T. Fumal (1994). Update to the Joyner Boore Fumal 1993 attenuation model, Communication to SCEC, April 1994. Cornell, C. A. (1968). Engineering seismic risk analysis, Bull. Seism. Soc. Am., 58,1583- 1606. Geomatrix (1992). Seismic ground motion study for. the west San Francisco Bay Bridge, Report to Caltrans, Contract No. 59N772. Idriss, I. M. (1991). Selection of Earthquake ground motions at rock sites, Report prepared for the Structures Div., Building and Fire Research Lab., NIST. Jennings (1994). Fault Activity map of Califonnia and adjacent areas, Calif. Div. Mines and Geology, Map No. 6. Petersen, M. D., C. H. Cramer, W. A. Bryant, M. S. Reichle, T. R. Toppozada, - Preliminary seismic hazard assessment for Los Angeles, Ventura, and Orange Counties, California affected by the January 17,1994 Northridge Earthquake, Bull. Seism. Soc. Am., In Press. Sadigh, K, C -Y Chang, N. A. Abrahamson, S. J. Chiou, and M. Power, (1993). Specification of long period motions: updated attenuation relations for rock site conditions and adjustment factors for near -fault effects, Proc. ATC 17-1., 59-70. Wells, D. and K.Coppersmith (1994). Updated empirical relationships among magnitude, rupture length, rupture area, and surface displacement, submitted to Bull. Seism. Soc. Am. Woodward -Clyde (1994). Seismic evaluation of southern California bridges, Final Report to Caltrans, 59N771. Working Group on California Earthquake Probabilities (1988). Probabilities of large earthquakes occurring in California on the San Andreas fault, U.S. Geological Survey Open File Report 88-398. Working Group on California Earthquake Probabilities (1995), Seismic hazards in Southern California: Probable earthquakes,1994 to 2024, Bull. Seism. Soc. Am., 85,379- 439. Youngs, R. R. K. Coppersmith (1985). Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates, Bull. Seism. Soc. Am., 75, 939-964. (-118.490, 34.352): CDMGv2, R. -c.,< 0.1 0.01 LU 0.001 a. CO MO 0.0001 0.00001 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Peak Ground Acceleration (g) Figure Ia. Probabilistic seismic hazard for horizontal peak acceleration. 10% chance of being exceeded in 250 -years corresponds to an annual probability of 0.0042. 11H Ill ill 111 -- ----- ------- 7-7-1 77 _Q ----- -- .. . ....... . . ...... . ... ..... .... . ...... 7"T 7-2 7 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Peak Ground Acceleration (g) Figure Ia. Probabilistic seismic hazard for horizontal peak acceleration. 10% chance of being exceeded in 250 -years corresponds to an annual probability of 0.0042. 10000 1000 100 10 (-118.490, 34.352): CDMGv2, Rock 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 * 1.4 1.5 Peak Ground Acceleration (g) Figure lb. Probabilistic seismic hazard for horizontal peak acceleration. 10% chance of being exceeded in 250 years corresponds to an average return period of 2380 years. 17 1r i I � i [ � � 111 � I r 1 it I � � T ;.. � rl i if -7 ! i !.. If L i. 4- ll �� Tii' if if, i if 'I � i i ti;i I':) I ,I II lii ! !i ii 1 !I Ilii i !! l; tai; T t 7 ifttt 4- J. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 * 1.4 1.5 Peak Ground Acceleration (g) Figure lb. Probabilistic seismic hazard for horizontal peak acceleration. 10% chance of being exceeded in 250 years corresponds to an average return period of 2380 years. (-118.490,34.352): CDMGv2, Rock - PGA =1.13 g p v.45 m i 0.4 0 0.35 c 0.3 u 02 0 0.15, 0.05 0 0.5 0.45 a 0.4 cu 0.35 0 C, 0.3 0 0.25 q 0.2 0 -0.15 c 0.1 U 0'05 L't 0 Figure 2. Deaggregated hazard at the 10% in 250 years level. 5.5 5 OU 25 E 20 015 10 5 0 0 (-118.490, 34.352): CDMGv2, Rock 0 0.5 1 1.5 2 2.5 Peak Acceleration (g) 11 2.5 2 1.5 0 .F n CL Lu 0.5 0 -0.5 -1 0 0.5 1 1.5 2 2.5 Peak Acceleration (g) Figure 3. Mean magnitude (M bar), distance (D bar), and number of standard deviations (epsilon bar) from the deaggregated hazard for the various levels of peak acceleration. 0.5 1 1.5 2 2.5 Peak Acceleration (g) emote= 0 0.5 1 1.5 2 2.5 Peak Acceleration (g) 11 2.5 2 1.5 0 .F n CL Lu 0.5 0 -0.5 -1 0 0.5 1 1.5 2 2.5 Peak Acceleration (g) Figure 3. Mean magnitude (M bar), distance (D bar), and number of standard deviations (epsilon bar) from the deaggregated hazard for the various levels of peak acceleration. 0.5 1 1.5 2 2.5 Peak Acceleration (g) Seismic Source Parameters for Site: -118.490, 34.352 Parameters common to all faults: b -value = 0.8 Magnitude recurrence = 1.0 Characteristic magnitude recurrence Parameters for individual faults: Santa Susana: ( CDM V' M 1 Slip rates.(mm/yr): 3.0 5.0 7.0 Weights for slip rates: 0.2 0.6 0.2 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.70 Weights for max. magnitude: 1.0 Fault mechanism: Reverse Sierra Madre: Slip rates (mm/yr): 0.5 3.0 4.0 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.80 Weights for max. magnitude: 1.0 Fault mechanism: Reverse San Gabriel: Slip rates (mm/yr): 0.5 1.0 1.5 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.75 Weights for max. -magnitude: 1.0 Fault mechanism: Strike -slip San Andreas: Slip rates (mm/yr): 34.0 Weights for slip rates: 1.0 Fault width (km): 12.0 Weight for fault width: 1.0 Maximum magnitude: 7.25 8.00 Weights for max. magnitude: 0.7 0.3 Fault mechanism: Strike -slip Palos Verdes: Slip rates (mm/yr): 1.0 3.0 4.0 Weights for slip rates: 0.2 0.6 0.2 Fault width (km): 12.0 Weight for fault width: 1.0 Maximum magnitude: 6.65 Weights for max. magnitude: 1.0 Fault mechanism: Strike -slip Elsinore: Slip rates (mm/yr): 3.0 5.0 7.0 Weights for slip rates: 0.25 0.5 0.25 Fault width (km): 12.0 Weight for fault width: 1.0 Maximum magnitude: 6.55 Weights for max. magnitude: 1.0 Fault mechanism: Strike -slip Whittier: Slip rates (mm/yr): 2.0 2.5 3.0 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 13.0 Weight for fault width: 1.0 Maximum magnitude: 6.55 Weights for max: magnitude: 1.0 Fault mechanism: Reverse Newport -Inglewood: 1.0 Slip rates (mm/yr): 0.1 0.8 Weights for slip rates: 0.3 0.5 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.80 Weights for max. magnitude: 1.0 Fault mechanism: Strike -slip Santa Monica: Slip rates (mm/yr): 0.4 2.5 Weights for slip rates: 0.3 0.4 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.45 Weights for max. magnitude: 1.0 1.0 0.2 4.0 0.3 Fault mechanism: Reverse/Oblique Malibu Coast: Slip rates (mm/yr): 1.0 2.0 Weights for slip rates: 0.4 0.4 Fault width (km): 13.0 Weight for fault width: 1.0 Maximum magnitude: 6.45 Weights for max. magnitude: 1.0 3.0 0.2 Fault mechanism: Reverse/Oblique Raymond: Slip rates (mm/yr): 0.2 1.0 2.0 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.35 Weights for max. magnitude: 1.0 Fault mechanism: Reverse/Oblique Oakridge: Slip rates (mm/yr): 0.2 1.0 2.0 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.35 Weights for max. magnitude: 1.0 Fault mechanism: Reverse/Oblique San Cayetano: Slip rates (mm/yr): 0.9 5.0 9.0 Weights for slip rates: 0.1 0.8 0.1 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.65 Weights for max. magnitude: 1.0 Fault mechanism: Reverse Ynez: Slip rates (mm/yr): 0.3 0.7 1.0 Weights for slip rates: 0.25 0.5 0.25 Fault width (km): 14.0 Weight for fault width: 1.0 Maximum magnitude: 6.75 Weights for max. magnitude: 1.0 Fault mechanism: Strike -slip White Wolf: Slip rates (mm/yr): 3.0 5.5 8.0 Weights for slip rates: 0.3 0.4 0.3 Fault width (km): 18.0 Weight for fault width: 1.0 Maximum magnitude: 7.25 Weights for max. magnitude: 1.0 Fault mechanism: Reverse