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NEIC Fast Moment Tensors

In an effort to improve data services, the National Earthquake Information
Center (NEIC) has begun a program, in cooperation with the IRIS Data Management
Center (DMC), to produce rapid estimates of the seismic moment tensor for most
earthquakes with a body-wave magnitude or surface-wave magnitude of 5.5 or
greater. Although this program is still undergoing testing and "fine-tuning", in
many cases an estimate of the moment tensor can be produced within 20 minutes of
the arrival of the "gophered" broadband P-waveform data from the IRIS DMC. The
resulting determination of earthquake depth, geometry, and size can be very
useful in the planning of post-earthquake studies, such as damage surveys and
the deployment of temporary seismic arrays. In some cases such information can
be crucial in the decision whether or not to issue a tsunami warning. Because of
the manner in which the data and the synthetic seismograms are aligned, the
method is insensitive to the effects of timing errors, epicentral mislocation,
and lateral heterogeneity.

The flow of data is as follows. An automatic process at the NEIC, using
real-time data from the U.S. National Seismograph Network (USNSN), identifies
phase arrivals, associates the data, and computes an origin time and hypocenter.
This information is sent by e-mail to the IRIS DMC where it triggers the Gopher
system. Four minutes of broadband data containing the P-arrival are retrieved
from the ring buffers of the "open" IRIS stations and transmitted to the NEIC by
Internet. These data are merged with the USNSN dataset and used to refine the
location and compute a body-wave moment tensor using a technique based on the
theory of optimal filter design. This solution is then broadcast by e-mail to a
list of subscribers. Because of the growing number of broadband seismic stations
with either real-time or dial-up capability, these preliminary solutions are
usually very similar to those produced later, using data from the entire
network.

Data Flow Chart

Fast
Moment Tensor Notification

Sample Fast Moment
Tensor Solution

Latest Fast Moment
Solutions

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U.S. Department of the
Interior | U.S. Geological
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URL: http://neic.usgs.gov/neis/FM/fast_moment.html

Contact: NEIC
Web Team
Last modification: Friday, 2004 January
23 16:02 MST