DOCSLIB.ORG

A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure by Gary S

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure by Gary S Bulletin of the Seismological Society of America, Vol. 102, No. 1, pp. 236–251, February 2012, doi: 10.1785/0120110041 A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure by Gary S. Fuis, Daniel S. Scheirer, Victoria E. Langenheim, and Monica D. Kohler* Abstract The widely held perception that the San Andreas fault (SAF) is vertical or steeply dipping in most places in southern California may not be correct. From studies of potential-field data, active-source imaging, and seismicity, the dip of the SAF is significantly nonvertical in many locations. The direction of dip appears to change in a systematic way through the Transverse Ranges: moderately southwest (55°–75°) in the western bend of the SAF in the Transverse Ranges (Big Bend); vertical to steep in the Mojave Desert; and moderately northeast (37°–65°) in a region extending from San Bernardino to the Salton Sea, spanning the eastern bend of the SAF in the Trans- verse Ranges. The shape of the modeled SAF is crudely that of a propeller. If con- firmed by further studies, the geometry of the modeled SAF would have important implications for tectonics and strong ground motions from SAF earthquakes. The SAF can be traced or projected through the crust to the north side of a well documented high-velocity body (HVB) in the upper mantle beneath the Transverse Ranges. The north side of this HVB may be an extension of the plate boundary into the mantle, and the HVB would appear to be part of the Pacific plate. Introduction In the Southern California Earthquake Center Commu- as the scenario M 7.8 earthquake of ShakeOut (Perry nity Fault Model (CFM; Plesch et al., 2007), the dip of the et al., 2008). San Andreas fault (SAF) is 90° in all but one location, as there is little subsurface data to modify this default value. The one exception is the San Gorgonio Pass SGP area of the eastern Tectonic Setting Transverse Ranges (Fig. 1), where surface constraints and seismicity have been used to justify a nonvertical dip in the Through the Transverse Ranges, the SAF strikes obli- model. In this study, we constrain the dip of the SAF by ana- quely to relative plate motion with bends at either end of lyzing near-surface and subsurface data, including potential the oblique stretch (Fig. 1). The Los Angeles Region Seismic field, seismic-imaging, and seismicity observations, from a Experiment (LARSE) transects (Fig. 1, profiles 4 and 5), number of locations in southern California. Surprisingly, which were recorded across this oblique section of the the SAF is significantly nonvertical in most places, dipping SAF, reveal interpreted fluid-lubricated midcrustal decolle- away from the bends at either end of its stretch through the ments originating at the SAF and extending southward into Transverse Ranges, where it is oblique to plate motion. The the Pacific plate. Reverse faults that splay upward from these overall shape of the SAF is similar to that of a propeller. The decollements have given rise to destructive earthquakes in M fault appears to extend or project through the crust to join the the Los Angeles region, including the 1971 w 6.7 San M north side of the well known upper-mantle high-velocity Fernando and 1987 w 5.9 Whittier Narrows earthquakes body (HVB) beneath the Transverse Ranges that has been (Fuis et al., 2001, 2003). A crustal root is observed beneath imaged with teleseismic tomography and Rayleigh waves. the Transverse Ranges centered, or nearly centered, on the These findings, if confirmed in further studies, would have SAF (Kohler and Davis, 1997; Fuis et al., 2001; Godfrey important implications for understanding the tectonics and et al., 2002; Fuis et al., 2007). The tectonic interpretation of strong- ground-motion potential from SAF earthquakes, such this crustal structure is that the upper crust, above the decol- lements, responds to convergence in this oblique section of *Now at Department of Mechanical and Civil Engineering, California the SAF by vertical and lateral motion, whereas the lower Institute of Technology, Pasadena, California 91125. crust is compressed into the crustal root (Houseman et al., 236 The San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure 237 Figure 1. Fault map of southern California and cross sections showing dipping San Andreas fault (SAF). Black and green lines, profiles discussed in paper; green dots, additional locations discussed. Profiles and locations are numbered sequentially from northwest to southeast, 1–15. Cross sections along black lines (1, 4, 5, 8, 10, 12, 13, 14, and 15) are shown as satellite diagrams with geographic location labels. Cross section 10 is reproduced with interpreted SAF (red line) from Jones et al. (1986; their fig. 3a). Cross sections 13–15 are reproduced with interpreted SAF (red lines) from Lin et al. (2007; their fig. 14). Green lines 2, 6, and 9 are locations of seismicity cross sections of Figure 9. Green line 7 is location of seismic-imaging profile through San Bernardino Valley (see text). Green dots 3 and 11 are locations, Three Points and Desert Hot Springs (see text). Heavy red line, San Andreas fault; reddish brown lines, other active faults (Jennings, 1994). Blue body, horizontal slice through upper-mantle high-velocity body at 110-km depth (see Kohler et al., 2003, their fig. 7A). Colors in cross sections 1, 8, and 12 are explained in Figure 3. Colors and symbols in cross sections 4 and 5 are explained in Figure 10. Abbreviations: CV, Coachella Valley; LAB, Los Angeles basin; SGP, San Gorgonio Pass; SS, Salton Sea. 2000; Fuis et al., 2001; Godfrey et al., 2002; Fuis throughout the crust, geophysical observations generally et al., 2007). constrain the SAF geometry in only the upper 5–15 km of the crust. For simplicity, we assume a constant dip as a function of depth for the SAF at the location of every Data Constraining Fault Dip constraint along its trace, except in the San Gorgonio Pass At a number of locations in southern California, we area where shallower indicators suggest a very gentle dip estimate the dip of the SAF from analysis of potential field, but deeper indicators suggest a steeper dip. In addition, seismicity, and seismic-imaging observations (Fig. 1). Where we linearly interpolate these dip values along the SAF trace possible, we assign an uncertainty to the dip values. Except between the constraint locations (Fig. 2), with interpolation for the LARSE observations that constrain the geometry distances that range from about 15 to 120 km. Because of the 238 G. S. Fuis, D. S. Scheirer, V. E. Langenheim, and M. D. Kohler Figure 2. (a) Plan view of dipping SAF model surface colored by depth; gray colors, unconstrained projections. Mountain ranges within Transverse Ranges (see Fig. 1): SGM, San Gabriel Mountains; SBM, San Bernardino Mountains; LSBM, Little San Bernardino Mountains; SAFOD, San Andreas Fault Observatory at Depth. (b) Oblique view of SAF surface from southeast. heterogeneous nature of our constraining observations and section (at Three Points; Fig. 1; Fig. 2a), gravity and because of the simplifications and interpolations required magnetic data also suggest a southwestward dip (30°–75°), to generate this dipping SAF model, we view the strength but uncertainty is greater. In the San Gorgonio Pass area, of this model to be simply its depiction of systematic and approximately 250 km southeast of the Big Bend cross sec- significant dip variations along the SAF. tion, gravity modeling indicates that the Banning strand of the SAF dips very gently (10°–15°) to the northeast in the Potential Field upper few kilometers (Griscom and Jachens, 1990; Langen- heim et al., 2005) (Fig. 2a). In this study we model two A published model of gravity data across the SAF in the vicinity of the Big Bend in the western Transverse Ranges additional profiles of magnetic data, at San Bernardino (Griscom and Jachens, 1990) indicates a southwestward dip and at Indio (Fig. 1, profiles 8 and 12), that indicate dips as shallow as 55° (Fig. 1, profile 1; Fig. 3a). The SAF is mod- of 37° and 65°, respectively (Fig. 3b,c). eled to a depth as great as 5 km. At 120–180 km northwest of A nearly continuous magnetic anomaly extends along this model location (at Cholame and the San Andreas Fault the SAF from the northwestern San Bernardino Mountains Observatory at Depth [SAFOD]); Fig. 2a], a steeper south- to Indio, averaging 200–500 nT at a nominal height of 300 m west dip is seen in the upper few kilometers of the crust, above terrain (Fig. 4; Griscom and Jachens, 1990). This 70°–90°from gravity data at Cholame (Griscom and Jachens, magnetic anomaly is predominantly positive and is spatially 1990) and 83° from drilling observations at SAFOD (Zoback associated with outcrop of units labeled as Precambrian et al., 2010). About 50 km southeast of the Big Bend cross igneous and metamorphic rock complex in the portions of The San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure 239 Figure 3. Block models for three sites along SAF. (a) Model of gravity data at the Big Bend of SAF (Griscom and Jachens, 1990). 3 Location is profile 1 on Figure 1. D, density differences (kg=m ) of upper crustal rocks of North American plate (NAM) compared 3 with Pacific plate (PAC, density 2670 kg=m ). (See also modeling of combined gravity and aeromagnetic data at Big Bend in Appendix A.) (b, c) Block models of magnetic data at San Bernardino and Indio sites on SAF from this study. Locations are profiles 8 and 12 on Figure 1.
Load more

Recommended publications
  • Introduction San Andreas Fault: an Overview
    Introduction This volume is a general geology field guide to the San Andreas Fault in the San Francisco Bay Area. The first section provides a brief overview of the San Andreas Fault in context to regional California geology, the Bay Area, and earthquake history with emphasis of the section of the fault that ruptured in the Great San Francisco Earthquake of 1906. This first section also contains information useful for discussion and making field observations associated with fault- related landforms, landslides and mass-wasting features, and the plant ecology in the study region. The second section contains field trips and recommended hikes on public lands in the Santa Cruz Mountains, along the San Mateo Coast, and at Point Reyes National Seashore. These trips provide access to the San Andreas Fault and associated faults, and to significant rock exposures and landforms in the vicinity. Note that more stops are provided in each of the sections than might be possible to visit in a day. The extra material is intended to provide optional choices to visit in a region with a wealth of natural resources, and to support discussions and provide information about additional field exploration in the Santa Cruz Mountains region. An early version of the guidebook was used in conjunction with the Pacific SEPM 2004 Fall Field Trip. Selected references provide a more technical and exhaustive overview of the fault system and geology in this field area; for instance, see USGS Professional Paper 1550-E (Wells, 2004). San Andreas Fault: An Overview The catastrophe caused by the 1906 earthquake in the San Francisco region started the study of earthquakes and California geology in earnest.
    [Show full text]
  • Region of the San Andreas Fault, Western Transverse Ranges, California
    Thrust-Induced Collapse of Mountains— An Example from the “Big Bend” Region of the San Andreas Fault, Western Transverse Ranges, California By Karl S. Kellogg Scientific Investigations Report 2004–5206 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director U.S. Geological Survey, Reston, Virginia: 2004 For sale by U.S. Geological Survey, Information Services Box 25286, Denver Federal Center Denver, CO 80225 For more information about the USGS and its products: Telephone: 1-888-ASK-USGS World Wide Web: http://www.usgs.gov/ Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. iii Contents Abstract ……………………………………………………………………………………… 1 Introduction …………………………………………………………………………………… 1 Geology of the Mount Pinos and Frazier Mountain Region …………………………………… 3 Fracturing of Crystalline Rocks in the Hanging Wall of Thrusts ……………………………… 5 Worldwide Examples of Gravitational Collapse ……………………………………………… 6 A Spreading Model for Mount Pinos and Frazier Mountain ………………………………… 6 Conclusions …………………………………………………………………………………… 8 Acknowledgments …………………………………………………………………………… 8 References …………………………………………………………………………………… 8 Illustrations 1. Regional geologic map of the western Transverse Ranges of southern California …………………………………………………………………………… 2 2. Simplified geologic map of the Mount Pinos-Frazier Mountain region …………… 2 3. View looking southeast across the San Andreas rift valley toward Frazier Mountain …………………………………………………………………… 3 4. View to the northwest of Mount Pinos, the rift valley (Cuddy Valley) of the San Andreas fault, and the trace of the Lockwood Valley fault ……………… 3 5.
    [Show full text]
  • Nehrp Final Technical Report
    NEHRP FINAL TECHNICAL REPORT Grant Number: G16AP00097 Term of Award: 9/2016-9/2017, extended to 12/2017 PI: Whitney Maria Behr1 Quaternary geologic slip rates along the Agua Blanca fault: implications for hazard to southern California and northern Baja California Abstract The Agua Blanca and San Miguel-Vallecitos Faults transfer ~14% of San Andreas-related Pacific-North American dextral plate motion across the Peninsular Ranges of Baja California. The Late Quaternary slip histories for the these faults are integral to mapping how strain is transferred by the southern San Andreas fault system from the Gulf of California to the western edge of the plate boundary, but have remained inadequately constrained. We present the first quantitative geologic slip rates for the Agua Blanca Fault, which of the two fault is characterized by the most prominent tectonic geomorphologic evidence of significant Late Quaternary dextral slip. Four slip rates from three sites measured using new airborne lidar and both cosmogenic 10Be exposure and optically stimulated luminescence geochronology suggest a steady along-strike rate of ~3 mm/a over 4 time frames. Specifically, the most probable Late Quaternary slip rates for the Agua Blanca Fault are 2.8 +0.8/-0.6 mm/a since ~65.1 ka, 3.0 +1.4/-0.8 mm/a since ~21.8 ka, 3.4 +0.8/-0.6 mm/a since ~11.8 ka, and 3.0 +3.0/-1.5 mm/a since ~1.6 ka, with all uncertainties reported at 95% confidence. These rates suggest that the Agua Blanca Fault accommodates at least half of plate boundary slip across northern Baja California.
    [Show full text]
  • A Pattern of Seismicity in Southern California: the Possibility of Earthquakes Triggered by Lunar and Solar Gravitational Tides
    A Pattern of Seismicity in Southern California: The Possibility of Earthquakes Triggered by Lunar and Solar Gravitational Tides David Nabhan Helen Keller wrote that the heresy of one age is the orthodoxy of the next, giving ample proof that although sightless, she possessed extraordinary vision. Moreover, it has been said that every new fact must pass through a crucible by which first it is ignored or ridiculed, then vigorously attacked, and finally accepted as though the truth had been apparent from the beginning. Earthquake prediction is no exception but for the anomaly that the first two stages have endured far longer than what the immense populations on the U.S. West Coast might hope to expect regarding a matter so important to their safety and welfare. Residents of Southern California have been left with a bewildering set of claims and counter-claims regarding this issue for many decades. While scientific data Seismic Gap Probabilities. Author's collection. can be presented any number of ways to say any number of things, there is another arbiter that, weighed alongside the conflicting findings, may allow fair-minded observers to come to their own cogent conclusions: history. There exists a long and verifiable record of events on the Pacific Coast and elsewhere David Nabhan, SDSU alumnus, is the author of Earthquake Prediction: Answers in Plain Sight (2012) and two other books on the subject. He is directing a public opinion campaign to impel the governor of California to convene the California Earthquake Prediction Evaluation Council for the purposes of determining the viability or fallibility of a seismic safety plan.
    [Show full text]
  • Geologic, Climatic, and Vegetation History of California
    GEOLOGIC, CLIMATIC, AND VEGETATION HISTORY OF CALIFORNIA Constance I. Millar I ntroduction The dawning of the “Anthropocene,” the era of human-induced climate change, exposes what paleoscientists have documented for decades: earth’s environment—land, sea, air, and the organisms that inhabit these—is in a state of continual flux. Change is part of global reality, as is the relatively new and disruptive role humans superimpose on environmental and climatic flux. Historic dynamism is central to understanding how plant lineages exist in the present—their journey through time illuminates plant ecology and diversity, niche preferences, range distributions, and life-history characteristics, and is essential grounding for successful conservation planning. The editors of the current Manual recognize that the geologic, climatic, and vegetation history of California belong together as a single story, reflecting their interweaving nature. Advances in the sci- ences of geology, climatology, and paleobotany have shaken earlier interpretations of earth’s history and promoted integrated understanding of the origins of land, climate, and biota of western North America. In unraveling mysteries about the “what, where, and when” of California history, the respec- tive sciences have also clarified the “how” of processes responsible for geologic, climatic, and vegeta- tion change. This narrative of California’s prehistory emphasizes process and scale while also portraying pic- tures of the past. The goal is to foster a deeper understanding of landscape dynamics of California that will help toward preparing for changes coming in the future. This in turn will inform meaningful and effective conservation decisions to protect the remarkable diversity of rock, sky, and life that is our California heritage.
    [Show full text]
  • 216166963.Pdf
    SEISMOLOGICAL RESEARCH ISSUES IN THE SAN DIEGO REGION Thomas H. Heaton and Lucile M. Jones U.S. Geological Survey 525 S. Wilson Ave. Pasadena, CA 911 04 June 1989 INTRODUCTION What is the nature of earthquake ground motions that can be expected in San Diego's foreseeable future? Although this is the most basic of questions underlying the adequate design of structures to resist earthquakes, answers to this question are disturbingly uncertain. A reasonable assumption is that future earthquake ground motions will be similar to those that have occurred in the past. When compared with San Francisco or Los Angeles, San Diego has historically experienced relatively mild earthquake shaking. Unfortunately, San Diego's written history is very short compared to the time scales of earthquake repetition. Are there sources of earthquakes that may cause damage in San Diego and what is their frequency? Mapping of geologic structures and the study of patterns of small earthquakes are the primary tools for recognizing potentially active faults. There are features in both the geologic structure and the seismicity that are suggestive of major active faults that could pose a serious hazard to San Diego. Furthermore, there is evidence that the rate of occurrence of small earthquakes has increased within the last 5 years when compared with the previous 50 years. However, these features are not well studied or understood. Even if the potential sources of earthquakes were well understood, the problem of anticipating the range of future ground motions is difficult. The nature of shaking from earthquakes is strongly affected by the nature of seismic wave propagation through complex geologic structures (path effects).
    [Show full text]
  • 1. NEOGENE TECTONICS of SOUTHERN CALIFORNIA . the Focus of This Research Project Is to Investigate the Timing of Rotation of T
    1. NEOGENE TECTONICS OF SOUTHERN CALIFORNIA. The focus of this research project is to investigate the timing of rotation of the Transverse Ranges and the evolution of the 3-D architecture of the Los Angeles basin. Objectives are to understand better the seismicity of the region and the relationships between petroleum accumulations and the structure and stratigraphic evolution of the basin. Figure 1 shows the main physiographic and structural features of the Los Angeles basin region, the epicenter of recent significant earthquakes and the our initial study area in the northeastern Los Angeles basin. Los Angeles basin tectonic model: Most tectonic models attribute the opening of the Los Angeles basin to lithospheric extension produced by breakaway of the Western Transverse Ranges from the Peninsular Ranges and 90 degrees or more of clockwise rotation from ca. 18 Ma to the present. Evidence of this extension includes crustal thinning on tomographic profiles between the Santa Ana Mountains and the Santa Monica Mountains and the presence in the Los Angeles basin of Middle Miocene volcanic rocks and proto-normal faults. Detailed evidence of the 3-D architecture of the rift created by the breakaway and the timing of the rift phase has remained elusive. The closing of the Los Angeles basin in response to N-S contraction began at ca. 8 Ma and continues today (Bjorklund, et al., 2002). A system of active faults has developed that pose significant seismic hazards for the greater Los Angeles region. Crustal heterogeneities that developed during the extension phase of basin development may have strongly influenced the location of these faults.
    [Show full text]
  • Imperial Irrigation District Final EIS/EIR
    Final Environmental Impact Report/ Environmental Impact Statement Imperial Irrigation District Water Conservation and Transfer Project VOLUME 2 of 6 (Section 3.3—Section 9.23) See Volume 1 for Table of Contents Prepared for Bureau of Reclamation Imperial Irrigation District October 2002 155 Grand Avenue Suite 1000 Oakland, CA 94612 SECTION 3.3 Geology and Soils 3.3 GEOLOGY AND SOILS 3.3 Geology and Soils 3.3.1 Introduction and Summary Table 3.3-1 summarizes the geology and soils impacts for the Proposed Project and Alternatives. TABLE 3.3-1 Summary of Geology and Soils Impacts1 Alternative 2: 130 KAFY Proposed Project: On-farm Irrigation Alternative 3: 300 KAFY System 230 KAFY Alternative 4: All Conservation Alternative 1: Improvements All Conservation 300 KAFY Measures No Project Only Measures Fallowing Only LOWER COLORADO RIVER No impacts. Continuation of No impacts. No impacts. No impacts. existing conditions. IID WATER SERVICE AREA AND AAC GS-1: Soil erosion Continuation of A2-GS-1: Soil A3-GS-1: Soil A4-GS-1: Soil from construction existing conditions. erosion from erosion from erosion from of conservation construction of construction of fallowing: Less measures: Less conservation conservation than significant than significant measures: Less measures: Less impact with impact. than significant than significant mitigation. impact. impact. GS-2: Soil erosion Continuation of No impact. A3-GS-2: Soil No impact. from operation of existing conditions. erosion from conservation operation of measures: Less conservation than significant measures: Less impact. than significant impact. GS-3: Reduction Continuation of A2-GS-2: A3-GS-3: No impact. of soil erosion existing conditions.
    [Show full text]
  • SSC 306 Thompson
    1 San Andreas and Other Fault Sources; Background Source SSC TI Team Evaluation Steve Thompson Diablo Canyon SSHAC Level 3 PSHA Workshop #3 Feedback to Technical Integration Team on Preliminary Models March 25-27, 2014 San Luis Obispo, CA PG&E DCPP SSHAC Study PG&E DCPP SSHAC Study 2 Overview of the Preliminary SSC Model SSC Elements: Key Fault Sources San Andreas and Other Regional Fault Sources Background Source PG&E DCPP SSHAC Study 3 San Andreas and Other Fault Sources San Andreas Fault Other 200-Mile Site Region Faults Goal: Goals: Capture maximum Complete SSC within 200-mi contribution of SAF Site Region Confirm past results about contribution of “other” faults PG&E DCPP SSHAC Study 4 San Andreas Fault Approach: Approximate UCERF3 Characterization Ten Sections in 200-mi Matched a composite “Participation MFD” Overestimates UCERF3 Solution PG&E DCPP SSHAC Study 5 San Andreas Fault Source Composite Participation MFD: P SC CR Pf Ch Cz BB MN MS (SB) = 1 2 3 4 5 6 7 8 9 풊 7.0, = 9 ( ) 푀 ≤ 푅푅푅푅푇푇푇푇푇 푀 � 푅푅푅푅푖 푀 푖=1 PG&E DCPP SSHAC Study 6 San Andreas Fault Source Composite Participation MFD: P SC CR Pf Ch Cz BB MN MS (SB) = 1 2 3 4 5 6 7 8 9 풊 = 1 2 3 4 5 풌 7.0 < 7.5, = 5 ( ) 푀 ≤ 푅푅푅푅푇푇푇푇푇 푀 � 푅푅푅푅푘 푀 푘=1 PG&E DCPP SSHAC Study 7 San Andreas Fault Source Composite Participation MFD: P SC CR Pf Ch Cz BB MN MS (SB) = 1 2 3 4 5 6 7 8 9 풊 = 1 2 3 4 5 풌 = 1 2 3 풏 > 7.5, = 3 ( ) 푀 푅푅푅푅푇푇푇푇푇 푀 � 푅푅푅푅푛 푀 푛=1 PG&E DCPP SSHAC Study 8 San Andreas Fault Source Composite Participation MFD: P Ch MS P CR Ch BB MS P SC CR Pf Ch Cz BB MN MS (SB) = 1 2
    [Show full text]
  • May 6, 2017 Demo
    IMPERIAL COUNTY AIR POLLUTION CONTROL DISTRICT https://en.wikipedia.org/wiki/Coyote_Mountains#/media/File:Coyote_Mountains.png May 6, 2017 Exceptional Event Documentation For the Imperial County PM10 Nonattainment Area An exceedance of the National Ambient Air Quality Standard (NAAQS) for PM10 at the Brawley, Calexico, El Centro, Niland and Westmorland monitor in California on May 6, 2017 May 6, 2017 Exceptional Event, Imperial County Table of Contents TABLE OF CONTENTS SECTION PAGE I Introduction .................................................................................................................................. 1 I.1 Public Notification [40 CFR §50.14(c)(1)] .............................................................. 3 I.2 Initial Notification of Potential Exceptional Event (INPEE) (40 CFR §50.14 (c)(2)) ................................................................................................... 3 I.3 Public Comment Process [40 CFR §50.14(c)(3)(v)(A-C)] .................................. 4 I.4 Mitigation of Exceptional Events [40 CFR §51.930] .......................................... 4 II Conceptual Model – A narrative that describes the event causing the exceedance and a discussion of how emissions from the event led to the exceedance at the affected monitor .................................................................................... 9 II.1 Description of the event causing the exceedance ............................................ 9 II.2 How emissions from the event led to an exceedance ...................................
    [Show full text]
  • EARTHQUAKE San Diego Danger Zones
    Article Published by “San Diego Reader”, Vol. 29, No. 9, March 2, 2000 EARTHQUAKE San Diego Danger Zones Ten years ago, the California Division of Mines and Geology came up with a scenario for what would happen if a magnitude 6.8 quake occurred on the Silver Strand Fault. Interstate 5 would “be closed from Balboa Avenue on the north to Palm Avenue on the south,” the report predicted. “Both I-5 and old Route 101 will also be closed where they cross each of the coastal lagoons south of Oceanside…. The Coronado Bridge will be closed.... For planning purposes, San Diego International Airport will be closed for all but emergency or vital operations for a period of two weeks due to liquefaction affecting runways, access, electric power supply…. Service along the [railway] line from Los Angles can be expected to be disrupted south of Oceanside… for three weeks after the earthquake.” Other predictions in the planning scenario added detail to the grim picture. Major SDG&E transmission substations “are particularly vulnerable to damage by earthquake shaking,” and conductor lines swinging together could cause many “burn downs.” Furthermore, “for planning purposes, the South Bay Power Plant should be considered to be out of operation for three days and at a significantly reduced capacity for one and a half weeks following the scenario earthquake.” Water mains bordering Mission Bay and San Diego Bay, the coastal areas, western Mission Valley, and the Otay Valley “will suffer several breaks per mile of pipe. Landslides in the Mt. Soledad area, coastal regions of La Jolla, the north wall of Mission Valley, and the edges of Otay Mesa may also damage facilities and distribution mains.
    [Show full text]
  • SEISMIC DESIGN PARAMETERS for New Buildings at San Bernardino Valley College, San Bernardino, California
    SEISMIC DESIGN PARAMETERS for New Buildings at San Bernardino Valley College, San Bernardino, California PROJECT DESCRIPTION San Bernardino Valley College (SBVC) is built on the San Bernardino Valley segment of the San Jacinto fault. The right-lateral strike-slip San Jacinto fault is thought capable of generating an upper bound earthquake (UBE) of moment magnitude Mw=7.3. Earth Consultants International (ECI) was asked to study the seismically induced ground motions at the SBVC site. The purpose of the project was to quantify the strong ground motion anticipated at SBVC due to local earthquakes. We explored the code-based methodology using a 10% probability of exceedance in 100 years. This is the definition of UBE which the California Geological Survey recommended at that time for critical structures. We also looked at fault-specific San Bernardino Valley College in relation to earthquakes and ground motions that could cause the major Quaternary faults in the region damage at SBVC. SOLUTION ECI determined an upper bound earthquake for SBVC based on geologic, tectonic, kinematic and seismo lo gical facto rs. We calcu lated th e probabilistic peak horizontal acceleration (PGA) and spectral acceleration with a 10 percent probability of exceedance in 100 years for all faults within 100 km of SBVC using site-specific data and published attenuation relationships. We developed 5 percent damped, uniform risk design response spectra, and compared it to the California Building Code (CBC) and International Council of Building Officials (ICBO) design code standards in effect then. International strong ground motion databases were searched to obtain time history records of ground displacements caused by recent large Average 5% damped uniform response spectra and earthquakes near the site, and source parameters spectra for different attenuation relations pertinent to SBVC.
    [Show full text]