Graduate student(s): Zack Washburn; Eric Hargrave
Undergraduate student(s): George Cadiente
University of California, Los Angeles: Collaborative Research
University of Arizona: Collaborative Research
Lawrence Livermore National Laboratory: Collaborative Research
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:
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
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.
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.
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.
or other one-time publication(s):
This is a simple presentation of images from the 1998 field season.
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.
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