OpenAMR - A JAVA-Based Computational Facility for Earthquake Rupture Forecasts Using Accelerating Moment Release

In conjunction with the RELM OpenSHA project, we are developing a regional earthquake probability estimator based on the Stress Accumulation (SA) model for accelerating moment release (AMR). The SA model suggests that precursory AMR is controlled by the evolution of the stress field preceding large events. Bowman and King [GRL, 2001] demonstrate that the pre-mainshock stress field, as indicated by a simple backslip model of the event, can be used to define the critical region that optimizes the precursory AMR signal. Recent work has shown that the Stress Accumulation AMR model can also be applied prospectively for forecasting future large events by calculating the pre-event stress field for a hypothetical earthquake scenario with a size and slip distribution consistent with geologic and geodetic evidence of the fault behavior. This stress field is then used to search for an AMR signal that would indicate the temporal proximity of the scenario event. We outline here the methodology being developed for a regional earthquake probability estimation package using the SA model for AMR. The approach combines a fault-based algorithm that utilizes geologically and historically supported rupture scenarios drawn from the SCEC Earthquake Rupture Forecast database, with a grid-based algorithm that searches for AMR preceding physically realistic scenario events occurring off of the fault network. The output of the analysis is a regional map of time-dependent earthquake probabilities. The package utilizes the object-oriented capabilities of JAVA programming both to interface with other components of OpenSHA, and to facilitate the direct comparison of the Stress Accumulation model forecasts with forecasts based on alternative search criteria. An alternative we are currently exploring for the grid-based algorithm uses circles rather than stress contours to search for precursory AMR. This will provide an assessment of the merit of the SA model for earthquake forecasting, independent of the merit of AMR.