Fore‐arc deformation controls frequency‐size distribution of megathrust earthquakes in subduction zones

Abstract

[1] Seismotectonic deformation in subduction zones seems to follow rather simple spatiotemporal patterns with fore-arc basins overlying the areas of large slip during quasiperiodic megathrust earthquakes. To study the possible coupling between long-term deformation and earthquake behavior, we use compressive granular wedges overlying a rate-and state-dependent frictional interface as analogue models of subduction zone fore arcs overlying a seismogenic megathrust. For different seismogenic zone geometries, we analyze deformation time series with respect to the accumulation of permanent strain and frequency-size distributions of episodic slip events equivalent to great (M > 8) earthquakes. We observe that permanent deformation in the wedges localizes at the periphery of unstable slip at depth over tens of simulated seismic cycles. For updip-limited seismogenic zone models, this leads to structural wedge segmentation characterized by an elastic domain overlying the zone of unstable basal slip. Along with the evolution of segmentation the frequency-size distributions of episodic slip events develop from more random, Gutenberg-Richter-like events (b value $0.6) toward more periodic, characteristic events (b value <0.1). Corresponding coefficients of variation (C v ) of recurrence intervals decrease from C v % 0.6 in deforming wedges to C v % 0.3 in segmented wedges. From the experiments we thus infer a positive feedback between fore-arc tectonics and megathrust seismogenesis which brings the system from a stochastic to a more deterministic state. Our experimental observations imply that the quasiperiodic recurrence of great subduction earthquakes evident from existing earthquake records is a long-term feature intrinsically related to the seismotectonic segmentation of the fore-arc wedges.Citation: Rosenau, M., and O. Oncken (2009), Fore-arc deformation controls frequency-size distribution of megathrust earthquakes in subduction zones,

Modeling Seismic Cycles of Great Megathrust Earthquakes Across the Scales With Focus at Postseismic Phase

“…Finally, we note that although this particular study is focused at seismic-cycle time scale predictions, the model is also ready to study the still poorly understood effects of the multiple seismic cycles on the longterm deformation of the upper plate (Rosenau & Oncken, 2009;Wang, 1995) as well as for investigation of effects of various subduction zone parameters on the maximal magnitude of earthquakes (Heuret et al, 2011;Schellart & Rawlinson, 2013).…”

Simple Crack Models Explain Deformation Induced by Subduction Zone Megathrust Earthquakes

“…Such a compressional feature can be greatly enhanced as the rupture front approaches the trench, because the ruptureinduced stress change generally scales with the rupture zone dimension (Fig. 9a,b), free-surface effects become more prominent, and triggered failure around the rupture front has more opportunity to reach the surface (Rosenau and Oncken, 2009;Ma, 2012). These transient features arising in dynamic rupture models are not present in the dynamic critical taper model (which is actually a quasi-static model).…”

Bathymetry of the Indonesian Sunda margin-relating morphological features of the upper plate slopes to the location and extent of the seismogenic zone

“…Such a lateral seismic velocity contrast is observed less distinctively on all other profiles further west off Java Kopp et al, 2002). A clear fault is not visible in coincident MCS data but one can speculate that there is a thrust (unresolved in existing MCS data) connecting the subduction fault with the seafloor at the downdip limit if the SZ described as protobackthrust by Rosenau and Oncken (2009) from analogue modelling.…”

“…Sibuet et al, 2007) splay faults connect the subduction fault with the seafloor along the slope break. Rosenau and Oncken (2009) found long-term permanent deformation at the updip and downdip limits on the SZ by analog modelling of great (M w ≥ 8) earthquakes. They termed the faults occurring at the updip limit of the SZ protothrust (a pair of seaward and landward dipping thrusts).…”

“…The backthrust in the MCS data of connects the subduction fault with the seafloor at the downdip limit of the SZ. We propose such a protobackthrust, as described by Rosenau and Oncken (2009) from analogue modelling, for the Java and Lesser Sunda margin (Fig. 6) at the lateral seismic velocity increase.…”