Spatial and Temporal Variations of Aftershock Activity of the 23 October 2011 Mw 7.1 Van, Turkey, Earthquake

Abstract

On 23 October 2011, an M w 7.1 earthquake struck the Van Lake region of eastern Turkey; causing vast damage in the cities of Van and Erciş. The mainshock was followed by a large number of aftershocks, which define a 60–70 km long and 30–35 km wide northeast–southwest-trending structure, in agreement with the source rupture mod- els derived for the main event. In this paper, we take advantage of this large data set to examine the spatial and temporal properties of the Van earthquake aftershock activity. We derive the spatial distribution of b-value of the Gutenberg–Richter law, as well as com- plementary seismicity parameters, along the surface projection of the fault plane. Recent studies have been published on the same issue, presenting controversial and sometimes opposite results. With respect to previous studies, we rely on a possibly higher quality catalog of relocated earthquakes. Furthermore, we adopt a more conservative approach, excluding from the analysis the first few days of data, until the M c reaches a stable com- pleteness threshold; finally, we conduct statistical tests in order to check the significance of the spatial and temporal variation of b-value across the fault plane. Calculations are made for the complete catalog and for two independent aftershock subcatalogs, after which a stable magnitude of completeness Mc is reached. For each catalog, we correlate the observed b-value patterns with slip distribution models of the mainshock obtained through the inversion of seismological and geodetic data. Overall, the b-values vary from 0.9 to 1.5 along the Van rupture fault zone. The higher b-values (> 1:1) are observed around the epicenter of the mainshock characterizing the higher coseismic slip area on the fault projection. Low b-values are concentrated at the periph- eral portion of the fault, away from high-slip patches. Moreover, the b-value distribution over the fault plane undergoes significant variation throughout the aftershock sequence.