34. Joint U.S.–Japan Program to Develop CoulombExpress: A Near-Real-Time
Online Earthquake Forecasting Tool for Emergency Responders and Scientists
There is considerable evidence that increases in the static Coulomb stress bring
faults closer to failure (Stein, 1999; King and Cocco, 2000). The spatial distribution
of Coulomb stress is generally found to be correlated with the distribution of
aftershocks, and with the triggering of subsequent main shocks (fig. 1). The
distribution of peak dynamic Coulomb stress may also correlate with aftershocks
(Kilb and others, 2002), and so static stress changes are not the only means
by which aftershocks are triggered. Nevertheless, the static Coulomb stress can
be rapidly and reliably calculated, and, if it is produced automatically and
made publicly available, it can serve to identify sites or faults with an increased
seismic risk following mainshocks. Today Coulomb analyses are published no sooner
than 13?onths after a large mainshock (McCloskey and others, 2005; Toda and
others, 2008). CoulombExpress is intended to produce them in near real-time.
 |
Figure 1. An
example of how CoulombExpress could contribute to seismic safety. During
the first 3 hours after the Landers earthquake, 3-4 M≥3 shocks clustered
at Big Bear, where the Landers earthquake was later calculated by Stein
and others (1992) to have increased the Coulomb stress by 1 bar. The M=6.5 Big
Bear quake (large open circle) stuck at this site 3 hr 8 min after the
Landers mainshock. Albeit with considerably less accuracy, CoulombExpress
would be able to deliver a warning before the second mainshock occurred. |
Under this opportunity the Fellow would help to develop a robust automatic system
to calculate Coulomb stress changes using real-time and near-real-time seismic
catalog information, such as magnitude, location, depth, and the two nodal planes
(fig. 2). The simplest module would use earthquake location, depth and magnitude
only, the information most rapidly available. The assumed plane of the earthquake
source fault and surrounding receiver faults (sites of aftershocks or successive
mainshocks) would be based on a smooth matrix of typical fault orientations based
on the distribution of active faults. For cases in which focal mechanism information
is available, we propose to calculate the Coulomb stress change on both nodal
planes, making the assumption that the receiver (or surrounding) faults have
the same strike, rake, and dip as the source faults (fig. 3). In addition, we
will resolve the stress changes on the mapped major active faults in their rake
directions (fig. 4).
 |
Figure 2. Flow diagram
of the CoulombExpress modules and products. The seismicity “Rate
Forecast” at bottom is based on Toda and others (2005); it will be the
focus of the Fellow’s work during Phase II. |
To test the feasibility of this opportunity, the research advisors have built
a matrix of assumed source and receiver fault planes for all of California
for this purpose, based on focal mechanisms and active faults. We calculate
the maximum stress change over a pre-specified depth range. The fault friction
coefficient and crustal elastic parameters are standardized. For resolving
stress on mapped active faults, we will use the new U.S. Geological Survey–California
Geological Survey–Southern California Earthquake Center California Reference
Fault Parameter Database and its equivalent in Japan.
Running Coulomb Express in both California and Japan will double the sample
of captured M≥5 earthquakes, enabling the Fellow to assess the strengths
and weaknesses of the system during the first test year. Because focal mechanism
information is automatically accessible from the Global CMT database, we
can also test CoulombExpress on M≥6 earthquakes around the globe. CoulombExpress
will run on a dedicated MATLAB server running a highly modified version of
Coulomb? (http://www.coulombstress.org/) (Toda and others, 2007).
 |
Figure 3. Stress changes for the 29 July 2008 Mw=5.4 Chino Hills earthquake
based on the initial Global CMT parameters. Both nodal planes (right and
left panels) are considered for sources and receiver faults. An example
pre-set calculation of the maximum stress changes over 510 km depth with
friction=0.4 is shown. |
 |
|
Figure 4. Stress imparted
by the 29 July 2008 Mw=5.4 Chino Hills quake to surrounding active
faults (left panel). The short blue vectors give the receiver fault
rakes, which are used in the calculation. MATLAB “fig” files
will be automatically generated, which can be spun and tilted by users
of MATLAB, as shown at right. |
The successful applicant will have a strong background in geophysics or seismology
and scientific computing, and be interested in spending considerable time
in Japan.
References
Kilb, D., Gomberg, J., and Bodin, P., 2002, Aftershock triggering by complete
Coulomb stress changes: Journal of Geophysical Research, v. 107, doi:10.1029/2001JB000202.
King, G.C.P., and Cocco, M., 2000, Fault interaction by elastic stress changes:
New clues from earthquake sequences: Advances in Geophysics, v. 44, p. 1–36.
McCloskey, J., Nalbant, S.S., and Steacy, S., 2005, Indonesian earthquake: Earthquake
risk from co-seismic stress: Nature, v. 434, p. 291.
Stein, R.S., 1999, The role of stress transfer in earthquake occurrence: Nature,
v. 402, p. 605–609.
Stein, R.S., King, G.C.P., and Lin, J., 1992, Change in failure stress on
the southern San Andreas fault system caused by the 1992 magnitude=7.4 Landers
earthquake: Science, v. 258, p. 1328–1332.
Toda, S., Stein, R.S., Richards-Dinger , K., and Bozkurt, S., 2005, Forecasting
the evolution of seismicity in southern California: Animations built on earthquake
stress transfer: Journal of Geophysical Research, v. B05S16, doi:10.1029/2004JB003415.
Toda, S., Stein, R.S., Lin, J., and Sevilgen, V., 2007, Coulomb 3, Graphic-rich
stress change and deformation software for earthquake, tectonic, and volcano
research and teaching; Mac/PC/Linux application, 60-p. user guide (http://www.coulombstress.org/).
Toda, S., Lin, J., Meghraoui, M., and Stein, R.S., 2008, 12 May 2008 M=7.9
Wenchuan, China, earthquake calculated to increase failure stress and seismicity
rate on three major fault systems: Geophysical Research Letters, doi:10.1029/2008GL034903.
Proposed Duty Station: Menlo Park, CA
Areas of Ph.D.: Geology, geophysics, seismology, computer science (candidates
holding a Ph.D. in other disciplines but with knowledge and skills relevant
to the Research Opportunity may be considered).
Qualifications: Applicants must meet one of the following
qualifications: Research
Geologist, Research Geophysicist, Computer Scientist
(This type of research is performed by those who have backgrounds for
the occupations stated above. However, other titles may be
applicable depending
on the applicant's background, education, and research
proposal. The final
classification of the position will be made by the Human Resources
specialist.)
Research Advisor(s):
Ross Stein, (650) 329-4840, rstein@usgs.gov;
Shinji Toda (DPRI, Kyoto University), +81 774-38-4234, toda@rcep.dpri.kyoto-u.ac.jp
Human Resources Office contact:
Candace
Azevedo, (916)?78-9393, caazevedo@usgs.gov
