Quantifying preparation process of large earthquakes: Damage localization and coalescent dynamics

Ilya Zaliapin, & Yehuda Ben-Zion

Submitted August 14, 2019, SCEC Contribution #9641, 2019 SCEC Annual Meeting Poster #089

We attempt to track and quantify preparation processes leading to large earthquakes with data of earthquake and acoustic emission (AE) catalogs using two complementary analyses. (a) Localization of brittle deformation manifested by evolving fractional volume with seismic activity, and (b) coalescence of events into clusters. We analyze AE data from several laboratory experiments and seismicity catalogs from Southern California (SoCal), Parkfield section of the San Andreas Fault (SAF), and region around the 1999 Izmit and Duzce earthquakes in Turkey.

Localization of deformation is evaluated via the fractional volume 0 < V(q) < 1 occupied by the fraction 0 < q < 1 of active voxels with mainshocks. The significance of the results is assessed using reshuffled catalogs. Analysis of the entire SoCal catalog shows a steady decrease of V(q) occupied by mainshocks with M > 2.5 during 1981 – 2018, most prominently in a quasi-linear region around the Imperial fault, Brawley seismic zone, SAF and Eastern California Shear Zone. Analysis around rupture zones of large earthquakes indicate decrease of V(q) (increased localization) prior to the Landers (1992, M7.3), Joshua Tree (1992, M6.1), and Duzce (1999, M7.2) mainshocks. We also observe ongoing damage production by the background seismicity around these rupture zones, and the July 2019 Ridgecrest sequence in SoCal, several years before their occurrences. In contrast, we observe increase of V(q) prior to the Parkfield (2004, M6.0) mainshock in the creeping section of the SAF. These findings are consistent with analysis of AE data.

The coalescence process is represented by a reverse time-oriented tree, with the last event being the root, constructed via the nearest-neighbor proximity approach. The coalescence index Z(t) quantifies the balance between the emergence of new events and merging of events to clusters. In AE experiments with different materials and loading conditions, the following failure stages are observed. (1) An early distributed phase with events that tend to fill the volume, Z(t) > 0. (2) Transition to instability where Z(t) fluctuates around zero. (3) A final short phase where Z(t) becomes negative leading to system size failure. Initial applications of the coalescence analysis to observed seismicity show promising results.

Key Words
large earthquakes, earthquake damage, localization

Zaliapin, I., & Ben-Zion, Y. (2019, 08). Quantifying preparation process of large earthquakes: Damage localization and coalescent dynamics. Poster Presentation at 2019 SCEC Annual Meeting.

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