查看更多>>摘要：The fact that the same fault may host different rupture or slip modes was partly attributed to the change in strain rate of the fault in previous studies. However, contradictory observations were obtained in the previous experimental studies, that is, the loading rate can promote or inhibit the rapid instability of faults. Although the two opposite effects of the loading rate were separately explained in the previous studies, the contradiction remains unresolved. Based on an experiment conducted on a granodiorite sample, we use the cumulative fault slip to quantitatively describe the slip-driven changes in fault properties and study the cross-effects of loading rate and cumulative fault slip on the pre-seismic rupture speed, unstable slip rate, and friction coefficient drop of the laboratory earthquakes (stick-slip events). The experimental results show that under the same loading rate, the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop of the stick-slip events increase with increasing cumulative fault slip. As a result, the loading rate has opposite effects on the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop under different amounts of the cumulative fault slip. This provides an explanation for the observation contradiction that the loading rate can promote or inhibit the rapid instability of the fault. The experimental results also reveal that the steady rupture speed is approximately proportional to the loading rate but weakly depends on the cumulative fault slip. Finally, the significance of the experimental results for understanding the earthquake and faulting mechanics is discussed.
查看更多>>摘要：I propose a new analysis method for determining the intraplate stress in geodynamic models using a series of numerical simulations of mantle convection in 3D spherical-shell geometry. In the present study, the intraplate stress was evaluated from numerically obtained velocity and stress fields of mantle, and quantitatively classified into nine types by analyzing the principal deviatoric stress axes and the "stress ratio," which is a continuous parameter accounting for the stress regimes. The sensitivity of model parameters and physical conditions associated with the basic characteristics of mantle convection, such as internal heating ratio, viscosity stratification, and temperature-dependent viscosity of the mantle as well as viscoplastic rheology that causes plate-like surface motion, on the intraplate stress regimes were studied. The results demonstrated that the radial viscosity structure of the mantle interior strongly affected intraplate stress regimes, and the combination of increased viscosity in the lower mantle and the low-viscosity asthenosphere enhanced the pure strike-slip faulting regime in the stable part of plate interiors. The temporally averaged toroidal-poloidal ratio (T/P ratio) at the top surface of mantle convection with surface plate-like motion and the mantle's viscosity stratification generally ranged similar to 20-40%, which is comparable to the observed T/P ratio of present-day and past Earth. Under such Earth-like surface conditions, normal faulting regime with strike-slip component or strike-slip regime with normal faulting component, as well as pure strike-slip faulting regime, were broadly found in the stable parts of the plate interiors. From the definition of the stress regime in the present study, strike-slip faults on the real Earth are likely to occur where the strike-slip faulting component is dominant in the present models. The analysis method proposed herein is effective for evaluating the intraplate stress in research target regions, for which observation data is insufficient to determine the intraplate stress.
Taymaz, TuncayYolsal-Cevikbilen, SedaIrmak, T. SerkanVera, Felipe...
24页
查看更多>>摘要：We resolve source mechanism and rupture process for the Neon Karlovasion, Samos Mw 7.0 earthquake that struck Greek-Turkish border regions on 30th October 2020 acquired from kinematic joint inversion of teleseismic body-waves and near-field strong ground-motion waveforms. The optimal kinematic finite-fault slip model indicates a planar E-W striking north-dipping normal faulting mechanism with strike phi = 270 degrees +/- 5 degrees, dip delta = 35 degrees +/- 5 degrees, rake lambda = -94 degrees +/- 5 degrees; centroid depth h = 11 +/- 2 km; duration of the source time function STF = 26 s and seismic moment M-0 = 3.34 x 10(19) Nm equivalent to Mw = 7.0. Our final finite- fault slip models exhibit two main asperities within a depth range from similar to 20 km to the surface. The dynamic rupture model exposes an initial heterogeneous stress distribution with variations up to 25 MPa. The near-field strong motion waveforms constrained the slip model suggesting up-dip and westward propagation of the bilateral rupture pattern with a maximum slip of 3.2 m, illuminated by back-projection (BP) analysis. The high-frequency (HF) back-projected rupture showed a predominantly E-W striking component (similar to 75%) with directivity of 277 degrees that propagates to the surface along a 60 km long and 24 km wide fault plane in 20 s at a slower speed range of 1.0-2.0 km/s. This well constrains the coseismic slip region where the aftershock sequence confirms distributed deformation. Our back-projection analyses elucidates a dominant HF rupture stage (0-13 s) tracked first on the epicentre area and further along the downdip in the region of maximum coseismic slip indicating similar to 15 km of persistent rupture. The latter HF emissions (13-20 s) remark a speed of about 3.0 km/s and a westward extension of the rupture up to 30 km from the preceding rupture segment to shorelines at the northeast of the Ikaria Island.
NSTL
Elsevier