GRiD MT (grid-based real-time determination of moment tensors) monitoring the long-period seismic wavefield

We have developed and implemented a new grid-based earthquake analysis system that continuously monitors long-period seismic wavefield of 20–50 s recorded by broadband seismometers. The new analysis system automatically and simultaneously determines the origin time, location and seismic moment tensor of seismic events within 3 min of their occurrence. This system has been in operation since 2003 at the Earthquake Research Institute (http://wwweic.eri.u-tokyo.ac.jp/GRiD MT/), and the locations and origin times are usually obtained within 3 s and 20 km away from the earthquake catalog values determined by the Japan Meteorological Agency (JMA). In addition, moment tensor solutions are comparable to the network solutions manually obtained. This new system should enable us to monitor long-period seismic wavefield continuously further to help identifying long-period (or low-frequency) events which are undetectable by the conventional monitoring of short-period seismic wavefields.