Landers Rupture — Sue on how monitoring networks evolved

The Southern California Seismic Network in Southern California dates back to the 1920s. It was installed by Caltech and the Carnegie institute way back when so the US Geological Survey was not in the earthquake monitoring business. It was really the purview of academic institutions including Caltech and networks were small there were, you know, small number of stations that weren't very well funded. When the US launched the national earthquake hazard reduction program in the 70s and then the USGS got involved as the lead agency for earthquake hazards and the lead agency for seismic monitoring. So, all of a sudden there were resources to significantly expand the seismic network. The USGS earthquake program was essentially born at that point. So the monitoring networks went from sort of fledgling running on a shoestring before the mid 70s to quite a bit more sophisticated. Now that said, as of ‘92 there were really two types of seismic instruments that were installed. The conventional seismic network instruments were very sensitive but if a big earthquake came along they'd get blown off scale. And then there was a separate class of instruments that were called strong motion instruments that were designed to only record large earthquakes. So you had these two different data streams with big earthquakes on the one hand and sensitive recordings of small earthquakes on the other and that really gave rise to two different disciplines within seismology. There were seismologists that looked at one type of the data or the other.