Microplate boundaries as obstacles to pre-earthquake strain transfer in Western Turkey: Inferences from continuous geochemical monitoring

Abstract Warm and hot spring water chemistry changes as well as soil gas radon release patterns have been monitored in Western Turkey, alongside regional seismicity, providing a multi-disciplinary approach. From January 2009 to May 2011, 33 earthquakes with ML between 4.0 and 6.0 occurred in this seismically very active region; the ML 6.0 earthquake occurred on 19 May 2011 in Simav town of Kutahya Province at a location midway between dense multidisciplinary monitoring networks of Marmara Region (MR) and the Aegean Extensional Province (AEP). We previously reported on noteworthy precursory anomalies prior to several earthquakes (ML ⩾ 4) in the MR and AEP, but no precursory anomaly was detected prior to the ML 6.0 event on 19 May 2011 in Simav, Kutahya Province, midway between dense multidisciplinary monitoring MR and AEP networks. Although these networks operate within the theoretical strain radii of this earthquake ( Dobrovolsky et al., 1979 ), no reliable anomaly were found. Geodetic studies based on GPS data have identified crustal blocks in this region. The epicentral area of the Simav event is located within a block tectonically separated from AEP and MR. Thus, we speculate that pre-earthquake strain accumulation within the Simav block did not effectively transfer to adjacent blocks where the MR and AEP networks are located, thereby providing an explanation for the absence of detectable anomalies. Moreover, prior to some earthquakes quadrant features of geochemical transients have been found; suggesting that soil radon anomalies appear in compressional quadrant(s) of pre-earthquake strain distribution.