Abstract
We present a critical appraisal of the role of subducted, medium (10–1000 km2) to giant (≥1000 km2) and heterogeneous, mud-rich mass transport deposits (MTDs) in seismic behavior and mechanisms of shallow earthquakes along subduction plate interfaces (or subduction channels) at convergent margins. Our observations from exhumed ancient subduction complexes around the world show that incorporation of mud-rich MTDs with a “chaotic” internal fabric (i.e., sedimentary mélanges or olistostromes) into subduction zones strongly modifies the structural architecture of a subduction plate interface and the physical properties of subducted material. The size and distribution of subducted MTDs with respect to the thickness of a subduction plate interface are critical factors influencing seismic behavior at convergent margins. Heterogeneous fabric and compositions of subducted MTDs may diminish the effectiveness of seismic ruptures considerably through the redistribution of overpressured fluids and accumulated strain. This phenomenon possibly favors the slow end-member of the spectrum of fault slip behavior (e.g., Slow Slip Events, Very Low Frequency Earthquakes, Non-Volcanic Tremors, creeping) compared to regular earthquakes, particularly in the shallow parts (T < 250 °C) of a subduction plate interface.
Highlights
Most large magnitude earthquakes (Mw ≥ 8.5) that occurred in the past are shown to have taken place along the frictional interface between two converging plates at subduction zones (e.g., Byrne et al, 1988; Scholz, 2002; Heuret et al, 2012; Scholl et al, 2015)
We examine heterogeneous, mud-rich mass transport deposits (MTDs hereafter) subducted along subduction plate interfaces, and discuss how they may affect the seismic behavior at convergent margins by strongly modifying the internal architecture and the mechanical – physical properties of subducted material
Our study shows that the subduction of medium to giant heterogeneous MTDs represents an additional factor in controlling seismic behavior by increasing the structural and compositional heterogeneity of subduction plate interfaces
Summary
Most large magnitude earthquakes (Mw ≥ 8.5) that occurred in the past are shown to have taken place along the frictional interface between two converging plates at subduction zones (e.g., Byrne et al, 1988; Scholz, 2002; Heuret et al, 2012; Scholl et al, 2015). Because it is highly difficult to decipher the internal architecture and composition of modern subduction plate interfaces through seismic reflection and tomography studies, our observations and interpretations presented here are largely based on on–land analogues of megathrust shear zones in ancient subduction complexes exposed in the Northern Apennines (Italy), the peri– Mediterranean region, the Appalachians, and the circum–Pacific region where the existence of fossil submarine MTDs is well documented These exhumed, ancient MTDs show strong similarities in size, distribution, recurrence interval, and run-out distance with modern submarine slide deposits in active continental margins (e.g., Camerlenghi and Pini, 2009; Urgeles and Camerlenghi, 2013; Ogata et al, 2014a, 2014b; Festa et al, 2014, 2016; Moscardelli and Woods, 2016)
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