Participant individuals: Graduate student(s): Zack Washburn; Eric Hargrave Undergraduate student(s): George Cadiente
Partner organizations: University of California, Los Angeles: Collaborative Research University of Arizona: Collaborative Research Lawrence Livermore National Laboratory: Collaborative Research Other collaborators:
Our Chinese colleagues from the Institute of Geomechanics of the Chinese Academy of Sciences in Beijing have collaborated with us scientifically and provided logistical support.
Activities and findings:
Research Activities: 1) The major effort in the last year was a 7 week field excursion along the central Altyn Tagh Fault (ATF) in western China. Arrowsmith along with UCLA graduate students Cowgill and Catlos and Chinese colleagues, mapped 5 sites along a 125 km reach of the central ATF. This work included mapping on airphoto and satellite image basemaps 10-20 km long reaches of the Quaternary geology along the fault zone. Within the mapping area, sites were chosen for more detailed work, which included topographic mapping using a total station, and sampling for numerical dating (14C, cosmogenic, and thermoluminesence). 6 detailed sites were investigated and the topographic and mapping data have been compiled and analyzed. Samples for numerical dating have been received in the US, but only the 14C sample has been analyzed. 2) Preparation of field equipment including a kite photography system for field operations in China. This tool permits us to make low altitude photographs of important landforms that record the Quaternary record of deformation along the Altyn Tagh fault. Pictures are posted at: http://www.public.asu.edu/~arrows/atf/atf98.html 3) Geo-rectification of Declassified Intelligence Satellite Photographs. These photographs are quite valuable as cheap alternatives to SPOT or other stereo satellite imagery. However, they are geometrically a bit difficult. We have spent a considerable effort at their geo-rectification and have nearly completed rectification of the first set. These images are quite useful for documenting the landforms and fault zone geometry in this region, and once they have been rectified, we can compile our geologic and geomorphic mapping in absolute coordinates and produce digital final maps and derivative products. Other data analysis and production has included preparation of basemaps of digital topography and seismicity for the region using GMT and GTOPO30. 4) Workshop and meeting participation has included consultation with colleagues and informal presentation at the Fall AGU meeting and the Altyn Tagh Fault working group meeting at UCLA in late February, 1999. As the results of our work become more complete in the next year, we expect to present them at the AGU and other meetings.
Research Findings: 1) Preliminary results are that the fault zone records significant evidence for major prehistoric earthquakes. The tectonic landforms that we have documented are world class examples of strike-slip related deformation. Trench investigations at one site provided the context for interpretation of a calibrated 14C date of 1245-1285 AD for the maximum age of the last earthquake or the minimum age for the penultimate event. Given the apparent slip rate of ~30 mm/yr in this area, a major earthquake might be expected about every 300 years or less (for a 9-m-slip event; assuming that all slip is released seismically and that the average recurrence calculated in this way is meaningful). The historic record for the region is probably less than 100 years, so the minimum age for the last event is 1900 A.D.
Research Training: Graduate and undergraduate student training in large scale logistics, image processing, and graduate student training in active tectonics and paleoseismology and numerical dating.
Education and Outreach: Arrowsmith presented a brown bag seminar to the ASU Geology Department that was attended by over 30 graduate students, faculty, and people from the community.
Journal Publications:
Book(s) or other one-time publication(s):
Internet Dissemination:
http://www.public.asu.edu/~arrows/atf/atf98.html
This is a simple presentation of images from the 1998 field season.
Contributions:
Contributions within Discipline:
Our preliminary findings help to focus inquiry on the Altyn Tagh fault and whether it is like other continental transform faults such as the San Andreas Fault. It is not very productive in instrumental seismicity, yet it has a high slip rate. Our investigations indicate that the last major earthquake along the central Altyn Tagh Fault was no more than about 700 years ago. This has implications for related studies of the current crustal deformation in the region.
Special Requirements for Annual Project Report:
Categories for which nothing is reported: Products: Journal Publications Products: Book or other one-time publication Products: Other specific product Contributions to Other Disciplines Contributions to Education and Human Resources Contributions to Resources for Science and Technology Contributions Beyond Science and Engineering Special Reporting Requirements Animal, Human Subjects, Biohazards