- © 2011 by the Seismological Society of America
In a recent Opinion in Seismological Research Letters, Jordan and Jones (2010) discussed the findings and recommendations of the International Commission on Earthquake Forecasting (ICEF) for operational earthquake forecasting convened by the Italian government following the 6 April 2009 L'Aquila Mw 6.3 earthquake, which killed 308 people in central Italy. “The goal of operational earthquake forecasting is to provide communities with information about seismic hazards that can be used to make decisions in advance of potentially destructive earthquakes” where “one of the outstanding challenges in the operational use of probabilistic forecasts is in translating them into decision-making in a low-probability environment” (Executive Summary, ICEF Report, Jordan et al. 2009).
An underlying assumption of the ICEF report is that earthquakes cannot yet be deterministically predicted, so that only probabilistic earthquake (low-probability) forecasts are possible. This “Second Opinion” discusses a new understanding of fluid-rock deformation that provides the opportunity for deterministic earthquake stress-forecasting. This removes one of the “outstanding challenges.” Deterministic forecasts can be made in a high-probability environment, which changes the emphasis of the ICEF report.
MONITORING FLUID-ROCK DEFORMATION AND EARTHQUAKE STRESS-FORECASTING
Shear-wave splitting (seismic birefringence) monitors the stress-aligned fluid-saturated microcrack geometry along the ray path. Fluid-saturated microcracks are compliant to changing conditions so that rocks are weak to shear stress. Consequently, the necessary stress accumulation before all large earthquakes has to build up over enormous volumes of rock, possibly world-wide and certainly plate-wide (Crampin and Gao 2010). The new understanding of fluid-rock deformation (Crampin 2006; Crampin and Peacock 2005, 2008) is that stress accumulation before large earthquakes can be monitored by analyzing shear-wave splitting throughout large volumes surrounding the impending earthquake source zone. Using shear-waves recorded above persistent swarms of small earthquakes, stress changes before large (or larger) earthquakes have been observed, and the times, magnitudes, …