REAL-TIME SHAKEMAPS

Abstract

Estimates of moment magnitude (M) and stress drops are required for various applications ranging from real-time ShakeMaps to the development of Ground Motion Prediction Equations (GMPE). In the context of the Brune model of ground motions, the moment controls long-period spectral amplitudes and the stress drop controls highfrequency spectral amplitudes. In Eastern North America, such estimates are most I commonly required for the small to moderate events that happen several times per year across a region. Most such events are not damaging but ShakeMaps are required to inform the public, and government or regulatory officials, as appropriate. This report illustrates the use of simulation based GMPEs, which are calibrated to the available empirical data, to obtain estimates of M and stress drop from ShakeMap ground motion parameters (PSA at 1 sec, PGA) on a sparse network. The simulations for the appropriate moment and stress are then used to create Googlemap based shaking maps for the region at the reference site condition. These generated ShakeMaps are a component of a post-earthquake rapid warning system. All the processed earthquake data, along with estimated source parameters and the ShakeMap are automatically published online (http://www.seismotoolbox.ca/ars/), and email notifications are sent to all subscribers giving information on motions experienced at specific sites of interest.