Japan Geoscience Union Meeting 2019

Presentation information

[E] Poster

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS04] New methods for seismicity characterization

Sun. May 26, 2019 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Francesco Grigoli(ETH-Zurich, Swiss Seismological Service), Aitaro Kato(Earthquake Research Institute, the University of Tokyo), Yosuke Aoki(Earthquake Research Institute, University of Tokyo), Claudio Satriano(Institut de Physique du Globe de Paris)

[SSS04-P02] Kinematic slip imaging of the Mw 3.3 earthquake in the St. Gallen 2013 geothermal reservoir, Switzerland, using an isochrone back projection approach

*Claudio Satriano1, Eszter Király-Proag2, Pascal Bernard1, Stefan Wiemer2 (1.Institut de Physique du Globe de Paris, France, 2.ETH Swiss Federal Institute of Technology Zurich, Switzerland)

Keywords:Earthquake Source, Earthquake Kinematics, Back Projection, Induced Seismicity

In most models and analyses, small earthquakes (i.e., M<4) are considered either point sources or "penny-shaped'' solid surfaces with homogeneous or isotropic source properties. While these assumptions may be valid, details of individual earthquakes are more complex. Due to the insufficient resolution of most monitoring networks, micro-earthquakes (M<2) must be still approximated as dislocation on penny-shaped surfaces. But in case of larger events (M>3) recorded on well-distributed local seismic stations, detailed space-time slip pattern within the rupture area can be imaged.

Here, we analyze slip distribution and rupture kinematics of a moderate induced event (ML 3.5) occurred in the St. Gallen geothermal reservoir (NE Switzerland) in 2013. To image the slip of such a small magnitude earthquake, we carry out a two-step procedure: (1) we deconvolve the propagation effects from the seismograms using an empirical Green's function resulting in relative source time functions (RSTF) at all seismic stations; (2) the RSTFs are back-projected to the fault plane using the position of equal time delays, i.e., isochrones.

Results reveal that the mainshock rupture propagates towards NNE from the hypocenter with an average velocity of about 2000 m/s. Spatio-temporal organization of fore- and aftershocks suggests that the mainshock released a previously less active portion of the fault and that the sequence is mainly stress-driven.

Applying this method in an operational environment could enable to quickly map seismic slip allowing assessment of fault asperities and structures involved in the reservoir creation process.