Did the 6 April 2009 L'Aquila Earthquake Fill a Seismic Gap?

Abstract

On 6 April 2009, a strong earthquake of magnitude Mw = 6.3 (red star in Figure 1) shook L'Aquila (southern Italy), causing massive damage and losses. Approximately 300 people died and more than 1,500 were injured. Following the mainshock there were many debates concerning the predictability of the earthquake. At present, earthquakes cannot be predicted (that is, there do not exist standard methods to determine with accuracy when the next earthquake will occur at a specific location and how large it will be) but only forecasted (that is, scientists can estimate the probability of occurrence of an earthquake of a given magnitude at a specific site) with a large degree of uncertainty. However, the analysis of intermediate- and short-term precursory phenomena, such as seismicity patterns ( e.g. , Kanamori 1981; Wyss et al. 1999), foreshock distributions ( e.g. , Jones and Molnar 1979; McGuire et al. 2005; Papadopoulos et al. 2010), and geochemical changes ( e.g. , Igarashi et al. 1995; Claesson et al. 2004) may allow us to make qualitative statements about the seismic potential of a given region (that is, about the likelihood of occurrence and the imminence of a large earthquake in an area) with little or no specification concerning the occurrence time and the size of the next strong event. Such statements can be useful for planning civil protection strategies. In this study, we analyze the space-time evolution of seismic strain rate in the area struck by the L'Aquila earthquake in search of possible seismicity patterns ( e.g. , spatial and temporal seismicity gaps), with the aim of providing new insights into the nature of this earthquake. More specifically, from the historical earthquake catalog we estimate the seismic strain rates as a function of space, for several distinct time intervals. Strain rates are estimated using …