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WITHDRAWN Precursory Deformation in the Lab – Effects of Roughness, Loading Rate and Effective Pressure

Description: 

WITHDRAWN Seismic and geodetic studies of large earthquakes at plate-bounding faults suggest

potential preparation phases potentially extending for months before main shocks

occur. Field observations show a varying deformation behaviour preceding failure

including aseismic creep and foreshock activity. Seismic foreshocks and aseismic slip

may or may not interact, low and decreasing seismic b-values may change in space

and time or remain roughly constant. A spatial correlation between inter-seismically

locked fault patches and co-seismic slip distribution has been suggested and is

corroborated by experimental studies.

Here we report on laboratory experiments performed at confining pressures of 30-

150 MPa on intact and faulted samples with different roughness, rock types (granite,

sandstone, shale) and varying boundary conditions (loading rate, geometry, fault prestress

and fluid pressure). Precursory deformation approaching failure is mainly

affected by loading conditions (displacement-driven shear vs injection-driven shear),

fault roughness, effective normal stress and load point velocity. For all faults, we

observe that enhanced loading/injection rates promote unstable stick-slip events.

Rough (heterogeneous) faults exhibit extended precursory slip and interplay of smallscale

high frequency acoustic emission events and slow confined ruptures during runup

to system-wide slip events. Smooth faults with polished surfaces typically display

short preparatory slip that is mostly aseismic. Slip events occur abruptly and are

initiated by few large acoustic events. Typical signatures derived from high-frequency

monitoring of picoseismic events include space-time changes in b-values, spatial

correlation of events (c-, d-values), changes in focal mechanism orientation patterns,

seismic moment release and partitioning between seismic and aseismic deformation.

Localization of deformation in slip patches during the precursory deformation phase

affects subsequent rupture and slip.

Session: Earthquake Preparation Across Scales: Reconciling Geophysical Observations With Laboratory and Theory

Type: Oral

Date: 4/20/2023

Presentation Time: 08:45 AM (local time)

Presenting Author: Georg Dresen

Student Presenter: No

Invited Presentation: Yes

Authors