Sebastien Chastin

New techniques for stress‐forecasting earthquakes

Abstract It is suggested that a stress‐monitoring site (SMS) in Central Taiwan would have recognised the build up of stress before the M 7.5 Chi‐Chi Earthquake so that the time and magnitude, but not necessarily the location, of the earthquake could have been stress‐forecast. SMSs exploit a new understanding of rock deformation, where stress‐induced modifications to fluid‐saturated grain‐boundary cracks and low aspect‐ratio pores (the most compliant elements of the rockmass) can be monitored by shear‐wave splitting in cross‐well seismics. To date, one M 5 earthquake has been successfully stress‐forecast using persistent swarms of small earthquakes as the source of shear waves. For that case, other precursory activity also allowed the approximate location to be predicted. Suitably persistent swarms of small earthquakes are extremely scarce, and reliable routine stress‐forecasting requires controlled‐source cross‐well seismics in SMSs between deep boreholes. This paper summarises the new understanding of rock deformation, the effects before earthquakes, the development of SMSs, and discusses the benefits that SMSs would have for stress‐forecasting the times and magnitudes of future large earthquakes in Taiwan.

Developing stress-monitoring sites

Theory, laboratory and field evidence reported elsewhere demonstrate that shear-wave splitting monitors the low-level pre-fracturing deformation of the crustal rock which is driven by the response of fluids in cracked rock.