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Abstract:
Waiting times distributions between successive earthquakes have extensively been studied to provide insights into the physical mechanism of seismogenesis and to effectively assess seismic hazard. While in tectonic seismicity the waiting times distribution is well-defined as the superposition of Omori-like aftershock sequences on correlated and/or random background activity, in induced seismicity associated with fluid-injections in the subsurface, the underlying physical mechanism remains ambiguous. Herein, we analyze the waiting times distributions in various cases of fluid-injection induced seismicity in deep geothermal reservoirs, as in the Cooper Basin (Australia), Basel (Switzerland), Soultz‐sous‐Forêts (France) and Espoo (Finland). In all cases that we study, the probability densities of waiting times present broad distributions with asymptotic power-law behavior, indicating clustering effects at intermediate and long-time scales. At short-time scales, however, clustering effects in most of the cases are either weak or absent, suggesting that seismic clustering due to aftershocks is missing. In the Habanero field (Cooper Basin), on the other hand, short-term clustering is also present, implying the interplay of various physical mechanisms in the evolution of induced seismicity. The observed scaling behaviour, in all the cases, can well be described with a stochastic model that incorporates nonstationarities and memory effects in the evolution of seismicity, contrasting a random Poisson process. AcknowledgementsThe research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 00256).
