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Announcement for USGS geodetic workshop - updating the U.S. National Seismic Hazard Maps

Date: 07/25/2012

Forwarded announcement from Mark Petersen, USGS:

The USGS is currently updating the National Seismic Hazard maps that are planned for release in 2014. These maps will be considered as the basis for future U.S. building codes. A geodetic workshop will be held October 18-19, 2012 (beginning in the afternoon on the 18th) in Newark, CA (San Francisco Bay area) at the corporate headquarters of RMS. In this workshop we will consider new western U.S. geodetic deformation models. This workshop will follow the California workshop, which will be held on October 17-18 (morning) and consider the new UCERF 3 model.

The workshop will consider questions related to how we translate GPS observations into earthquake rate models. Geodetic data have been collected over the past several decades and most scientists participating in our workshops are of the opinion that the National Seismic Hazard Map models should incorporate those data. The geodetic models consider slip rates with geologic constraints on the San Andreas Fault System, Cascadia Subduction Zone, Walker Lane, Wasatch Fault, and other regional faults, with the remaining strain rate budget being allocated to surrounding areas. These residual strain rates may constrain the amount of off-fault earthquake activity included in the hazard source model. While the geodetic model provides a regional tectonic loading-rate, not all of the total moment rate is seismic so the ratio of aseismic/seismic slip rates is also a critical parameter needed to define the earthquake rates used in the hazard analysis. Some of the new models have total moment rates that exceed the geologic moment rates. This may be caused by the uncertainty in the seismogenic depth of the fault/background earthquake sources. Another important issue for seismic hazard assessment involves the stationarity of slip rates through time (transient effect and clustering in deformation rates). This leads to the question of whether faults can turn off or on or can exhibit temporal clustering patterns. These discrepancies and issues will be discussed at the Geodetic workshop.

We invite all interested parties to participate in this workshop. To register for the workshop please go to the website: https://geohazards.usgs.gov/mailman/listinfo/nshmp-geodesy . We look forward to discussions on geodetic input to these new earthquake source models.


Yuehua Zeng, Wayne Thatcher, and Mark Petersen