THE WHITTIER FAULT TREND: CROSS SECTIONS, STRUCTURE MAPS, AND WELL TOPS IN THE MAJOR OIL PRODUCING AREA OF THE NORTHEASTERN LOS ANGELES BASIN, by Tom Bjorklund, Search and Discovery Article #10038 (2003)

THE WHITTIER FAULT TREND: CROSS SECTIONS, STRUCTURE MAPS, AND WELL TOPS IN THE MAJOR OIL PRODUCING AREA OF THE NORTHEASTERN LOS ANGELES BASIN*

*Adaptation for online presentation of selected results of the author’s research for Ph.D. dissertation. A more comprehensive compilation of the author’s work is presented on CD-ROM in Search and Discovery CD-ROM Series #1, entitled The Whittier Fault Trend in the Major Oil Producing Area of the Northeastern Los Angeles Basin: Interpretation and Data. This publication is available from Search and Discovery sd@datapages.com and AAPG Bookstore (http://bookstore.aapg.org).

Understanding the deep structure of the Los Angeles basin is critical to the assessment of the seismic hazard as well as the future petroleum potential in one of the most densely populated regions in the United States. In the center of the basin, that deep structure is hardly known because over 6.4 km of Pliocene and younger rocks have buried the rocks that record the early history of the basin. The acquisition of the modern seismic data that might reveal the deep structure has not been feasible in this densely populated area. Fortunately, just 50 km to the east, evidence of the character of the structure of the deep Los Angeles basin is accessible in the outcrops and wells of the Puente Hills area of the northeastern Los Angeles basin (NELAB). There, Miocene and older rocks have been uplifted along the Whittier fault by as much as 4.5 km since ca. 7-8 Ma by N-S shortening that is linked to the development of the San Andreas fault system. Thousands of oil wells have been drilled in the area, some to depths of more than 3 km.

Two recent papers together describe an integrated 3-D analysis of this unique window into the Los Angeles basin with the aim of developing a well-constrained geologic model to help in understanding the structural development and seismicity of the region. Bjorklund and Burke (2002) focus on a huge quantity of surface and subsurface data along the Whittier fault and introduce a three-phase model for the evolution of the active fault. Their model establishes relationships between early rifting and later folding and reverse faulting. Bjorklund, et al. (2002) review the evidence for Miocene extension in the NELAB. In that study, relationships established among volcanic rocks, active faults and mid-crustal structures revealed by P-wave tomography indicate that crustal heterogeneities may localize areas of high seismicity. This publication is a set of newly prepared maps, cross sections and tables that substantially supplement the material presented in the two already published papers. Other topics addressed in this publication include: (1) Sources and quality of data, (2) elaborations on previously published interpretations, and (3) aspects that may warrant further study.

The interpretations in this publication are based on data from a wide range of sources, including a significant body of interpreted data that has been held by oil companies. By making the original data of this publication readily accessible in a digital format, we hope to facilitate additional research that will result in the refinement and the enlargement of the existing database and greater public availability of privately held data