AN ABSTRACTOF THE THESIS OF Hirovuki Tsutsumi for the degree of Doctor of Philosophy in Geosciences presented on March 7. 1996. Title: Evaluation of Seismic Hazards From the Median Tectonic Line Japan and Blind Thrust Faults in the Los Angeles Metropolitan Area. California. Abstract approved: Robert S. ''eats This thesis analyzes active geologic structures in densely populated areas in Japan and southern California based on geological, geophysical, and paleoseismological observations. Chapter 2 discusses segmentation and paleoseismology of the Median Tectonic Line, Japan. We identified 12 geometric segments along the Median Tectonic Line separated by discontinuities such as en echelon steps, bends, changes in strike, and gaps in the surface trace. The recurrence interval and surficial offset for surface-rupturing earthquakes at four individual sites on the Median Tectonic Line in Shikoku Island are 1000-3000 years and 5-8 in, respectively. Part of the fault zone ruptured most recently during or after the 16th century A.D.; this rupture may be correlated to the 1596 Keicho- Kinki earthquake. Chapter 3 discusses active and late Cenozoic tectonics of the northern Los Angeles fault system, California. We mapped the subsurface geology of the northern Los Angeles basin from the City of Santa Monica eastward to downtown Los Angeles, based on an extensive set of oil-well data. The northern Los Angeles fault system developed through an early to late Miocene extensional regime and a Plio-Pleistocene contractional regime. The uplift of the oxygen isotope substage 5e marine terrace at Pacific Palisades and an estimated dip greater than 45° suggest a dip-slip rate as large as 1.5 mm/yr for the Santa Monica Mountains blind thrust fault, a rate considerably smaller than a previous estimate. Chapter 4 discusses the geologic setting of the 1971 San Fernando and 1994 Northridge earthquakes, two of the most devastating earthquakes in southern California history. We mapped the subsurface geology of the northern San Fernando Valley that lies at the updip projection of the two earthquake faults. The San Fernando Valley is underlain by a series of north-dipping blind thrust faults. The thick accumulation of the Plio-Pleistocene Saugus Formation in the Sylmar basin and Merrick syncline is a surface expression of the south-dipping 1994 Northridge thrust that is overlain by the north- dipping 1971 San Fernando fault at a depth of -5 km. © Copyright by Hiroyuki Tsutsumi March 7, 1996 All Rights Reserved Evaluation of Seismic Hazards From the Median Tectonic Line, Japan and Blind Thrust Faults in the Los Angeles Metropolitan Area, California by Hiroyuki Tsutsumi A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed March 7, 1996 CommencementJune 1996 Doctor of Philosophy thesis of Hiroyuki Tsutsumi presented on March 7. 1996 APPROVED: Major Professor, represen4ni Geosciences Chair of Department of Geosciences Dean of Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. ids,. i4tJtQAA/)wi Hiroyuki Tsutsumi, Author ACKNOWLEDGMENT I would like to thank the major professor, Dr. Robert S. Yeats, for his guidance throughout the graduate study at Oregon State University. I am also grateful to the committee members, Drs. Philip L. Jackson, LaVerne D. Kulm, Robert J. Lillie, and Charles L. Rosenfeld for their guidance and encouragement. Dr. Gary J. Huftile provided instructions on basic techniques of subsurface geologic analysis. I greatly benefited from discussions with Cheryl Hummon, Craig L. Schneider, and Thomas L. Wright. I would also like to acknowledge continuous guidance and encouragement by Dr. Atsumasa Okada of Kyoto University and Dr. Takashi Nakata of Hiroshima University, Japan. I have been supported by the United States Information Agency as a Fulbright scholar. Researches in chapters 3 and 4 were funded by grants from the National Earthquake Hazards Reduction Program, National Science Foundation, and Southern California Earthquake Center. Subsurface data for these studies were provided by the petroleum industry. CONTRIBUTION OF AUTHORS The three main chapters of this thesis are manuscripts that are in press, submitted, or to be submitted to geoscience journals. Robert S. Yeats was the Principal Investigator of research projects presented in Chapters 3 and 4, and was closely involved with each of the investigations. Specific contributions to these manuscripts by authors are listed below. Chapter 2: Atsumasa Okada and Hiroyuki Tsutsumi have collaborated in geomorphic mapping and trench excavations of the Median Tectonic Line since 1988, through which most of the data presented in this paper were gathered. Hiroyuki Tsutsumi is the primary author of the paper. Chapter 3: Hiroyuki Tsutsumi analyzed the geology west of the Newport- Inglewood fault zone and is the primary author of the paper. Robert S. Yeats evaluated a slip rate of the Santa Monica Mountains blind thrust fault based on topographic profiles constructed from a digital elevation model. He also identified many problems addressed in this paper. Cheryl Hummon and Craig L. Schneider analyzed the geology east of the Newport-Inglewood fault zone in their MS theses, and part of their analysis was incorporated in this paper. Gary J. Huftile provided guidance into the subsurface geologic mapping and regional geology throughout this project. Chapter 4: Hiroyuki Tsutsumi analyzed the geology in the Pacoima oil field and surrounding areas and is the primary author of the paper. Robert S. Yeats analyzed the geology of the Cascade oil field and closely supervised the work by Tsutsumi. TABLE OF CONTENTS Page Chapter 1: Introduction ..........................................................................1 Chapter 2: Segmentation and Holocene Surface Faulting on the Median Tectonic Line, Southwest Japan .......................................................................... 3 Abstract ................................................................................... 4 Introduction .............................................................................. 4 Regional Setting ......................................................................... 5 Methodology ............................................................................. 9 Segmentation Model .................................................................. 11 Paleoseismology ...................................................................... 17 Tsunden Segment ............................................................ 17 Chichio Segment ............................................................. 22 Okamura Segment ............................................................ 25 Sea of Iyo Segment .......................................................... 26 Discussion ............................................................................. 27 Correlation of the Most Recent Surface-Rupturing Earthquake on the MTL to a Historical Earthquake .................................... 27 Probable Rupture Lengthof Surface-Rupturing Earthquakes on the MTL ................................................................... 29 Space-Time Distribution of Holocene Faulting ........................... 30 Recurrence Interval of Large Earthquakes at Individual Sites Along the MTL ............................................................... 33 Conclusion ............................................................................. 34 TABLE OF CONTENTS(Continued) Page Acknowledgments....................................................................35 Chapter3:Active and Late Cenozoic Tectonics of the Northern Los Angeles FaultSystem,California......................................................................37 Abstract ................................................................................. 38 Introduction ............................................................................ 39 Regional Setting.......................................................................41 Overview of the Study Area................................................41 Stratigraphy...................................................................44 Major Geologic Structures...........................................................47 Santa Monica Fault System.................................................47 Structures East of the West Beverly Hills Lineament .................... 55 Newport-Inglewood Fault Zone............................................59 Discussion.............................................................................60 Interaction Between the Northern Los Angeles Fault System and Newport-Inglewood Fault Zone ....................................... 60 Slip Rate of Pliocene to Early Pleistocene Structures Based on Analysis of Growth Strata 61 Late Quaternary Slip Rate of the Santa Monica Mountains Blind Thrust Fault ............................................................ 62 Late Cenozoic Tectonic Evolution of the Northern Los Angeles Basin ........................................................................... 66 Early to lateMiocene extensional tectonics.......................66 TABLE OF CONTENTS(Continued) Page Early Pliocene to early Pleistocene contractional tectonics.....71 Contemporary tectonics............................................72 Conclusion.............................................................................73