The Guerrero Accelerograph Network

This project is a joint investigation of
the Seismological Laboratory, UNR, and the Instituto de Ingenieria, UNAM.

Principle Investigators: Dr John Anderson and Ing. Roberto Quaas

Network Description

A major factor in the motivation for installing the Guerrero accelerograph network was the report by Iwan (1978), recognizing the importance of international collaborations to gather strong motion data from the near field of strong earthquakes. The report recognized that Mexico is one of the most active parts of the western hemisphere. The Guerrero network then grew naturally out a long-ongoing collaboration between Jim Brune, a founder of the network, and several scientists in Mexico.

The Guerrero network consists of 30 digital strong motion accelerographs in Guerrero, and neighboring states, Mexico. The network was designed to record accelerograms from large earthquakes on part of the Mexico subduction thrust. The network is located above a mature seismic gap (see map and space-time diagram), and within the next few years it has as high probability as any strong motion network in the world to record one or more earthquakes with magnitude near 8.

The project is significant for the United States because the geometry of subduction in Guerrero is quite similar to that along the Pacific Northwest, in the Cascadia subduction zone. Data from Guerrero will provide significant insight into the type of ground motions that can be expected in Seattle, Portland, and all along the Pacific coast of the United States from Cape Mendocino, California to the Canadian border. The subduction zone has a smaller dip than the subduction zones in Alaska and Puerto Rico, but the data is still relevant for predicting ground motions there. The project is significant for several other seismically active regions as well. In particular the subduction zone in Guerrero is providing relevant data for prediction of ground motions from the subduction zones in Japan, Indonesia, Taiwan, Chile (and the rest of Central and South America).

Anderson et al submitted a paper summarizing the first twenty years of operation to the 8th US National Conference on Earthquake Engineering.

The 30 original sites for the Guerrero accelerograph network were selected to be on the best rock available, consistent with the network geometry and secondary siting criteria. A few of the stations have been moved, but the objectives of the network have not been compromised. The digital instruments have operated extremely well since 1985, producing data in a quality and quantity that exceeded our original expectations. The Instituto de Ingenieria has upgraded the equipment since the original installation, so now nearly all stations have digital accelerographs with resolution of 19 bits or higher.

At the end of December, 2004, the network had produced over 3700 accelerograms from over 1800 earthquakes. It has recorded 105 earthquakes with magnitude 5.0 or greater within the network. For earthquakes of magnitude 5.0 or greater in Guerrero, the probability of being recorded on the network is essentially 1.0. This probability drops to about 50% for magnitude 4.0. Completeness of earthquake coverage can be viewed graphically.

The network has recorded ten earthquakes with magnitude of 7.0 or greater, an average of one every two years. The most important records to date have come from the Sept 19 and Sept 21, 1985 (Ms8.1 and 7.6), April 25, 1989 (Ms6.9), Oct 24, 1993 (Ms 6.7), Sept 14, 1995 (Ms 7.4), July 15, 1996 (Ms 6.5), Jan. 11, 1997 (Mw 7.1), and Jan. 22, 2003 (Mw 7.4) earthquakes. At smaller magnitudes, the network has produced an excellent set of seismograms from earthquakes with magnitudes 4.2 and up. It has also recorded numerous seismograms from events with magnitudes down to 3.0 and below, although these smaller events rarely trigger more than a few stations.

"This material is based upon work supported by the National Science Foundation under Grant No. CMS 0000050. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation."