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.
Fast Moment Tensor Notification
Sample Fast Moment
Tensor Solution
