MONTHLY DINNER MEETING
Date: Wednesday, February 15, 2006
Note: This is a Wednesday night meeting.
Location: Steven's Steak House, 5332 Stevens Place, Commerce, California
Time: 6:00 p.m.-Social Hour; 7:00 p.m.-Dinner; 7:45 p.m.-Presentation
Cost: $30 per person with reservations, $35 at the door, $15 for students with a valid Student ID
Reservations: Please call (323) 889-5366 or email rmunro@mactec.com
SPEAKER: Miles D. Kenney, Ph.D.
TOPIC: Late Quaternary deformation and sedimentation history, Coachella fan area located between the Mecca Hills and Indio Hills, and northeast of the San Andreas fault, eastern Coachella Valley, California.
ABSTRACT
Evidence provided by fault trenching and geologic mapping over 5400 acres within the Coachella fan area located northwest of the Mecca Hills, southeast of the Indio Hills and northeast of the San Andreas fault indicates variations of sedimentation, erosion, and seismically induced deformation during the Quaternary. Sedimentary units in the region include (from oldest to youngest), a middle to lower member of the Palm Spring Formation, a member of the Canebrake Formation, upper member of the Palm Spring Formation (mid-Pleistocene), Ocotillo Conglomerate (late Pleistocene), and younger fan deposits within current drainages (latest Pleistocene to recent). Small exposures of faulted and steeply folded middle or lower Palm Spring Formation suggest that transpressive deformation similar to deformation seen in the Mecca and/or Indio Hills occurred between these two localities prior to and or during deposition of the mid-Pleistocene Canebrake member. The transpressive style deformation subsided prior to deposition of the upper Palm Spring Formation which consists of low energy fluvial and lacustrine deposits that crossed east of the current location of the San Andreas fault. Soon after deposition of the upper Palm Spring Formation (~700,000 years ago), the unit was tilted toward the southwest, which coincides with deposition of coarse grained overlying Ocotillo Conglomerate upon the deformed upper Palm Spring Formation. Just prior to and during deposition of the Ocotillo Conglomerate, a series of closely spaced (10s of feet), dominantly southwestern dipping normal listric faults striking approximately parallel to fan contours accommodated southwestward transport. The normal faults appear listric with basal shear surfaces within clay and liquefiable zones in primarily Palm Spring Formation. Contemporaneous tilting and folding occurred as these units as they moved toward the southwest (downslope) and buttressed up against the northeastern side of San Andreas fault down slope. The lateral spreading along normal and stacked parallel to bedding basal shear surfaces along weak zones was likely attributed to a combination of factors including down-slope dip of the Palm Spring Formation, unit composition, abundant groundwater during the Pleistocene, and strong local ground shaking. This style of deformation decreased dramatically in the latest Pleistocene but continues on a few relatively widely spaced (100's feet) oblique strike-slip normal faults suggesting either deeper basal shear surfaces (deeper groundwater) utilized for southwest transport during lateral spreading, and/or tectonic faults associated with local kinematics. Thus, the majority of the late Pleistocene faults in this region are associated with gravitational and ground shaking forces, and to a lesser degree to tectonic far-field forces.
SPEAKER BIOGRAPHY
Ph.D., 1999, Geological Sciences, University of Oregon, Bachelor of Science, 1989 Geological Science with emphasis in Chemistry, San Diego State University (graduated cum laude)
Dr. Kenney has over eight years of project experience in the performance of geotechnical engineering investigations and over nine years of experience in geological research and investigations with an emphasis on seismic hazards. Areas of extended study included Quaternary geology, structural geology, igneous and sedimentary petrology, geomorphology, seismology, kinematics, fault hazard evaluation, and neotectonics.
Dr. Kenney has managed many fault hazard investigations throughout southern California, which have included trenching, field mapping, evaluation of morphostratigraphic terrace and fan deposits, surveying, drilling, fault slip vector determinations, estimates of anticipated moment magnitude and slip per event, and aerial photograph interpretation.
Dr. Kenney's geotechnical experience includes slope stability evaluations and mitigation, large to small scale diameter drilling, geologic mapping, percolation rate determinations, seepage evaluations, cross-sections, drafting, report preparation, and large and small rough and post grading projects. Specific client experience has included residential, commercial, educational, transportation, and municipal projects.
