Near real- time simulations of global CMT earthquakes

We have developed a near real- time system for the simulation of global earthquakes. Prompted by a trigger from the Global Centroid Moment Tensor (CMT) Project, the system automatically calculates normal- mode synthetic seismograms for the Preliminary Reference Earth Model, and spectral- element synthetic seismograms for 3- D mantle model S362ANI in combination with crustal model Crust2.0. The 1- D and 3- D synthetics for more than 1800 seismographic stations operated by members of the international Federation of Digital Seismograph Networks are made available via the internet (global.shakemovie.princeton.edu) and the Incorporated Research Institutions for Seismology Data Management Center (IRIS; iris.edu). The record length of the synthetics is 100 min for CMT events with magnitudes less than 7.5, capturing R1 and G1 at all epicentral distances, and 200 min for CMT events with magnitudes equal to or greater than 7.5, capturing R2 and G2. The mode simulations are accurate at periods of 8 s and longer, whereas the spectral- element simulations are accurate between periods from 17 to 500 s. The spectral- element software incorporates a number of recent improvements, for example, the mesh honours the Moho as a first- order discontinuity underneath the oceans and continents, and the performance of the solver is enhanced by reducing processor cache misses and optimizing matrix-matrix multiplication. In addition to synthetic seismograms, the system produces a number of earthquake animations, as well as various record sections comparing simulated and observed seismograms.