ANALYSIS OF SHALLOW RESISTIVITY PROFILES ACROSS THE SAN JOSE FAULT ON THE CALIFORNIA STATE POLYTECHNIC UNIVERSITY, POMONA CAMPUS A Thesis Presented to the Faculty of California State Polytechnic University, Pomona In Partial Fulfillment Of the Requirements for the Degree Master of Science In Geological Sciences By Kevin J. Chantrapornlert 2016 SIGNATURE PAGE THESIS: ANALYSIS OF SHALLOW RESISTIVITY PROFILES ACROSS THE SAN JOSE FAULT ON THE CALIFORNIA STATE POLYTECHNIC UNIVERSITY, POMONA CAMPUS AUTHOR: Kevin J. Chantrapornlert DATE SUBMITTED: Winter 2016 Geological Sciences Department Dr. Jascha Polet ___________________________________________ Thesis Committee Chair Geological Sciences Dr. Jonathan Nourse ___________________________________________ Department Chair Geological Sciences Dr. Stephen Osborn ___________________________________________ Associate Professor Geological Sciences Dr. Nicholas Van Buer ___________________________________________ Assistant Professor Geological Sciences Dr. Bryan Murray ___________________________________________ Assistant Professor Geological Sciences ii ACKNOWLEDGEMENTS I would like to thank my advisor and committee chair, Dr. Jascha Polet. Without her guidance and direction, this research would not be possible. Her continued dedication and care for her students is unparalleled. Professors I would also like to thank all those who have helped me conduct my research: Homar Colin, Terry Cheiffetz, Raymond Ng, Mike Vadman, Rosa Nguyen, Julie Leiva, and Stacey Petrashek. Without the help of these friends, I would never have been able to conduct the fieldwork required for my project. iii ABSTRACT The San Jose fault extends from the San Jose hills into the Pomona Valley. The 1988 and 1990 Upland earthquakes have been attributed to this fault and large segments may rupture in a bigger future event. Sections of the fault are considered to run through the campus of California State Polytechnic University, Pomona. Resistivity surveys were conducted across several areas where the fault has been inferred to exist on the basis of boreholes, trenches, and gamma-ray spectrometer surveys by a geotechnical engineering report (GeoCon, 2001). Resistivity surveys measure how conductive the subsurface is to electrical current and therefore may be used to detect groundwater, lithologic changes, and offset due to faulting. The surveys consisted of 24 electrodes in a Wenner configuration with a spacing between 1-5 m. The data was processed using Geotomo’s RES2DINV software to obtain 2D profiles of resistivity. Surveys were performed before and after rainfall, whenever possible, to analyze its possible effect. The resulting images were interpreted to provide an enhanced understanding of the fault as it dissects the campus. Agreements as well as incongruities were found when comparing our resistivity models with the geotechnical cross-sections. Interpretations of several resistivity profiles suggest the presence of water, pounding up against the fault. Based on our results, we suggest that some fault traces may be located ~20 m south of their reported location. At the corner of Camphor Lane and University Drive, profiles with little lateral variation suggest that it is unlikely that the fault runs through this area. iv TABLE OF CONTENTS SIGNATURE PAGE ......................................................................................... ii ACKNOWLEDGEMENTS ................................................................................ iii ABSTRACT ...................................................................................................... iv LIST OF TABLES ............................................................................................. vii LIST OF FIGURES .......................................................................................... viii CHAPTER 1: Introduction ................................................................................ 1 Tectonic Overview ................................................................................. 3 The San Jose Fault ............................................................................... 6 The San Jose Fault on the Cal Poly Pomona Campus .............. 10 Research Approach ............................................................................... 16 CHAPTER 2: Surveying Methods, Equipment, and Software ......................... 19 Resistivity .............................................................................................. 19 Examples of Past Fault Studies Using Resistivity ...................... 24 Wenner Arrays ...................................................................................... 34 Equipment ............................................................................................. 36 Procedure .............................................................................................. 37 Data Processing Software ..................................................................... 46 Inversion Software ................................................................................ 48 CHAPTER 3: Inversion Results and Interpretations ........................................ 52 Site 1 .................................................................................................... 52 Site 2 ..................................................................................................... 60 v Site 3 .................................................................................................... 77 Site 4 .................................................................................................... 84 Site 5 .................................................................................................... 94 Site 6 .................................................................................................... 98 Site 7 .................................................................................................... 105 CHAPTER 4: Conclusions ............................................................................... 110 Closing Remarks ................................................................................... 112 Recommendations for Future Work ...................................................... 113 References ...................................................................................................... 116 Appendix A ...................................................................................................... 124 vi LIST OF TABLES Table 1. Resistivity values for various rocks, soils, and chemicals. .................... 20 vii LIST OF FIGURES Figure 1. The San Jose fault ................................................................................... 2 Figure 2. Map depicting the San Jose fault (red line) and the surrounding areas ....................................................................................................... 4 Figure 3. A seismicity map of the area surrounding the San Jose fault .................. 5 Figure 4. The San Jose fault acts as a barrier to flow ............................................. 7 Figure 5. The offset of the effective base of fresh water due to faulting ................. 8 Figure 6. Earthquakes in Upland California between 1981-1989 recorded by the Southern California Seismic Network ............................................... 9 Figure 7. San Jose fault location as interpreted by GeoCon (2001) .................. 12 Figure 8. Boreholes in the vicinity of Site 1 ........................................................... 14 Figure 9. A plot of the spectrometer readings used by GeoCon to help determine the location of the San Jose fault ......................................... 15 Figure 10. A plot of the spectrometer readings used by GeoCon to help determine the location of the San Jose fault ......................................... 16 Figure 11. The slip zone of the fault ...................................................................... 18 Figure 12. Current flow in a simplified homogeneous half space ......................... 21 Figure 13. Current flow between two electrodes ................................................... 23 Figure 14. An ERT image of the Los Avestruces Central High in Argentina shown above its interpreted coss-section ............................................. 27 Figure 15. An ERT image utilizing a Wenner-Schlumberger array in the Kamenička municipal in the Czech republic ......................................... 28 Figure 16. A cross section of the High Agri Valley Basin in Southern Italy ........... 29 viii Figure 17. ERT across the San Bartolo fault scarp in the Percordillera of western Argentina ................................................................................. 30 Figure 18. An ERT survey across the Tierra Blanca fault in the city of San Miguel Uspantán, Guatemala ............................................................... 31 Figure 19. An ERT profile across the Geleen fault in the Belgian Maas River valley ..................................................................................................... 32 Figure 20. An electrical resistivity tomography (ERT) profile with the corresponding interpreted geologic cross-section across the Yalguaraz fault in the Central Andes of Argentina33 Figure 21. An ERT survey utilizing a dipole-dipole array ..................................... 33 Figure 22. A Wenner electrode array with 24 electrodes. ..................................... 35 Figure 23. Survey 063005A conducted