Dynamic Stress Drop for Selected Seismic Events at Rudna Copper Mine, Poland

Abstract

In this paper, we report on an analysis of rupture processes of mining-induced events using the Empirical Green Function approach. The basic goal of this analysis is to estimate the dynamic stress drop-the quantity describing frictional forces at a slipping fault plane during the unstable part of an earthquake. The presented results cover 40 selected events with magnitude M w ranging between 2.1 and 3.6 occurring in the Rudna copper mine (Poland) between 1996 and 2006. The spatial extent of the seismic network operated by the mine enabled us to estimate not only the dynamic stress drop but also the rupture velocities for most of the events studied. The results are analyzed in terms of correlations of the ratio of static to dynamic stress drop with other parameters characterizing the rupture processes. We also pose a question about the conditions of occurrence of over-and undershooting stress drop mechanisms. For all but two events, the estimated dynamic stress drop ranges between 0.1 and 4 MPa and is dominated by lower values. There are only two exceptions when it reaches the level of the order of 10 MPa. The reliability of these two exceptional cases is low, however. The rupture velocity, needed for dynamic stress drop calculation, was estimated from observed directivity effects. The obtained values ranged between 0.2 and almost 0.9 shear wave velocity, with dominating low velocities. The ratio of static to dynamic stress drop does not clearly correlate with the seismic scalar moment, source radius estimated according to Madariaga's model, or static stress drop. It only positively correlates with the rupture velocity and ranges from values lower than 1 (undershooting mechanisms), mostly for slow events, up to values larger than 1 (overshooting mechanisms) for the majority of fast events. For all events with overshooting-type mechanisms, the estimated rupture velocity V r was larger than half of the S-wave velocity V s : On the other hand, for the undershooting-type events the associated rupture velocity was in most cases smaller than 0.6 V s and large rupture speed was observed only in a few cases for this type of events.

Recurrence Time Analysis of the 1883 (Mw 8.6 ~ 9.1) Paleo Megathrust Earthquake in West Bengkulu, Sumatra, Indonesia, Using Plate Kinematic Model for Supporting Mitigation Program

“…Δσ is an important variable in the dynamic model as the basic parameter to estimate the recurrence time of an earthquake. (Dębski 2018) explains that to describe the stress release effects, seismology uses three basic parameters namely the static stress drop, the Coulomb stress transfer, and the dynamic stress drop.…”