AEG Great Basin Monthly Meeting—December 6

Association of Environmental & Engineering Geologists, Great Basin Chapter, Monthly Meeting

Speaker: Dr. John Wakabayashi, 2017–2018 Jahns Lecturer
Date: Wednesday, December 6 (change from usual monthly meeting date)—RSVP by December 4
Topic: Evolution of step-overs and bends along strike-slip faults: Implications for seismic hazards assessment

Abstract: Step-overs along strike-slip faults have been traditionally considered to grow in size and cumulative slip accommodation as more slip accrues on the parent strike-slip fault. In such a model with greater slip, a pull-apart basin grows larger and deeper and a restraining step-over generates more uplift and exhumation. Inspection of step-overs of the San Andreas fault system suggests that step-overs migrate with respect to material formerly within them. This requires progressive formation of new transfer structures in the direction of migration. This process appears to operate from the meters/tens of meters scale of sag ponds and small push-up blocks to multi-kilometer scale basins and uplifted welts, with the Mendocino Triple Junction region being perhaps the largest scale structure of this sort proposed. Migrating step-overs result in inversion at all scales from thrusted sag pond deposits to inverted large-scale sedimentary basins. This style of step-over migration complicates assessment of long-term displacement on strike-slip faults because the zone of displacement is commonly much broader than the active strand, and this also applies to more recent displacement and earthquake history. Accordingly, siting of paleoseismic trenches needs to address this potential complexity in order to most optimally capture the full fault slip rate (for fault-parallel trenches) and most complete earthquake histories (for fault-crossing trenches). In addition the migrating step-over mechanism leads to propagation of some fault stands and the dying out of activity on others. This may result in some faults with a large cumulative displacement that have little or no late Quaternary activity whereas some immature strands with little geomorphic expression may accommodate significant slip rate.

Based on the following published papers (but the paleoseismic implications are not in these papers):

Wakabayashi, J., 2007, Step-overs that migrate with respect to affected deposits: Field characteristics and speculation on some details of their evolution: in Cunningham, W.D., and Mann, P., eds. Tectonics of strike-slip releasing and restraining bends in continental and oceanic settings.  Geological Society of London Special Publication 290, p. 169-188.

Wakabayashi, J., Hengesh, J.V., and Sawyer, T.L., 2004, Four-dimensional transform fault processes: progressive evolution of step-overs and bends: Tectonophysics, v. 392, p. 279-301.

Biography: John Wakabayashi is a San Francisco Bay Area native who moved to Fresno in 2005 to begin his academic career as a geology professor at California State University, Fresno. He received his B.A. in Geology in 1980 from UC Berkeley, and his PhD in Geology in 1989 from UC Davis (advisor: Eldridge Moores). He is a Professional Geologist (California) and a Fellow of the Geological Society of America.

After graduating from Davis he worked as an engineering and environmental geologist for 16 years (1989-2005), the last 13 years as an independent consultant based in Hayward, California, before becoming an academic. He worked on a variety of different types of projects, including seismic hazard evaluation/paleoseismology, slope stability, engineering and forensic petrography, naturally occurring asbestos, and two Superfund projects on which his primary specialty was evaluation of ambient concentrations of metals of environmental concern in soils and rock. He was a member of the Working Group on California Earthquake Probabilities.

When not doing project work (i.e. when not billable), he conducted independent research, some of which derived from his project work, but most of which dealt with more esoteric research issues such as subduction initiation processes, metamorphic P-T paths and metamorphic contrasts as tectonic indicators, emplacement of ophiolites, subduction interface processes and development of subduction complexes, evolution of orogenic belts, development of strike-slip fault systems, and long time and length scale geomorphology. He incorporated academic research of his own and others into all of his project work, trying to bridge the academic-applied geology gap from the standpoint of a practitioner. After becoming an academic he has continued his efforts to bridge this gap, with realization that the vast majority of geology professors have never been employed in the engineering and environmental geology profession that most geology graduates will work in. He incorporates both his professional and research experience into his teaching so as to better prepare students for professional careers, as well as providing a foundation for students who wish to undertake graduate study.

His research has resulted in 82 published papers and over 100 abstracts tied to presentations at major geoscience meetings. The breadth of his research has broadened rather than narrowed over time. In spite of the wide range of research interests, the geology of that beguiling train wreck of rocks known as the Franciscan Complex of coastal California remains his chief interest and the many aspects of mélanges have become his main focus since 2009. At Fresno State he teaches non-major introductory geology, geology major undergraduate courses in petrology, geomorphology, and structural geology, graduate courses on active tectonics/seismic hazard analysis and orogenic belt tectonics, and his bread-and-butter undergraduate course in advanced geologic field mapping (he makes his students map Franciscan along with landslides, flights of stream terraces and some potentially active faults). He has supervised or is supervising a large number of graduate and undergraduate student researchers, and this includes a number of students from outside of Fresno State.

Outside of geology and beer (an amateur brewer since 1994), he is probably best known for his experience trout fishing in the backcountry (must be hiked to) of California, having launched casts into over 750 different lakes, about 700 of these in the Sierra Nevada; 2015 was an especially good summer. His strength and fitness routine that prepares him for his fieldwork and recreational hiking (and burns off some of the beer), as well as holding his body together for his return to playing basketball, has also gained some notoriety. This routine includes excessively long plank sessions and multiple repetitions of muscle ups.

(Hotel name change – same location)

The Social Hour is sponsored by Silver State Analytical Labs – Open Bar.

Members: $25.00
Non-Members: $29.00
Students: $15.00
Student Dinners are sponsored for the first four who sign up for the meeting. All other students will be charged $15.

Please give us a 48 our cancellation notice if you are not able to attend.

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