Subduction zone megathrust earthquakes

Abstract

Subduction zone megathrust faults host Earth's largest earthquakes, along with multitudes of smaller events that contribute to plate convergence. An understanding of the faulting behavior of megathrusts is central to seismic and tsunami hazard assessment around subduction zone margins. Cumulative sliding displacement across each megathrust, which extends from the trench to the downdip transition to interplate ductile deformation, is accommodated by a combination of rapid stick-slip earthquakes, episodic slow-slip events, and quasi-static creep. Megathrust faults have heterogeneous frictional properties that contribute to earthquake diversity, which is considered here in terms of regional variations in maximum recorded magnitudes, Gutenberg-Richter b values, earthquake productivity, and cumulative seismic moment depth distributions for the major subduction zones. Great earthquakes on megathrusts occur in irregular cycles of interseismic strain accumulation, foreshock activity, main-shock rupture, postseismic slip, viscoelastic relaxation, and fault healing, with all stages now being captured by geophysical monitoring. Observations of depth-dependent radiation characteristics, large earthquake slip distributions, variations in rupture velocities, radiated energy and stress drop, and relationships to aftershock distributions and afterslip are discussed. Seismic sequences for very large events have some degree of regularity within subduction zone segments, but this can be complicated by supercycles of intermittent huge ruptures that traverse segment boundaries. Factors influencing variability of large megathrust ruptures, such as large-scale plate structure and kinematics, presence of sediments and fluids, lower-plate bathymetric roughness, and upper-plate structure, are discussed. The diversity of megathrust failure processes presents a suite of natural hazards, including earthquake shaking, submarine slumping, and tsunami generation. Improved monitoring of the offshore environment is needed to better quantify and mitigate the threats posed by megathrust earthquakes globally.

Thermal Structure of the Forearc in Subduction Zones: A Comparison of Methodologies

“…A spectrum of seismic and aseismic deformation (including regular earthquakes along the plate interface and in the subducting and overlying plates, low-frequency tremor, and slow slip along the interface) also occur in the forearc region (e.g., Bilek & Lay, 2018;Ide et al, 2007;Rogers & Drager, 2003). The spatial distribution of these processes depends significantly on the thermal structure of the forearc as chemical reactions and rock rheology are strongly sensitive to temperature.…”

Revised earthquake sources along Manila Trench for tsunami hazard assessment in the South China Sea

“…How and where earthquake rupture will occur on a plate boundary is challenging to forecast (Bilek and Lay, 2018;Satake and Atwater, 2007). A comprehensive understanding of a single megathrust behavior may be impractical since the seismic cycle is typically in the order of hundreds and thousands of years, much longer than instrumental records.…”

“…Globally, the eventual ruptures of some unexpected fault locations keep surprising scientists (Bilek and Lay, 2018). We've seen partial ruptures of fully locked megathrusts (Konca et al, 2008;Qiu et al, 2016;Ruiz et al, 2014;Schurr et al, 2014), and piecemeal breaks in the center of perceived seismic gaps (e.g.…”

“…Great efforts have been made to investigate the physical parameters that characterize subduction zones with regard to the geometry, geology and dynamics (Schellart and Rawlinson, 2013). Systematic analysis of collections of great earthquakes globally indeed suggests that some of the physical parameters do play key roles in controlling the rupture characteristics (Bilek and Lay, 2018;Bletery et al, 2016;Schellart and Rawlinson, 2013).…”

Shallow Megathrust Slip During Large Earthquakes That Have High P Coda Levels

“…Most of Earth's largest earthquakes involve rupture of plate boundary megathrust faults in subduction zones (e.g., Allen & Hayes, 2017;Bilek & Lay, 2018;Kanamori, 2014;Lay, 2016;Lay et al, 2012). The seismogenic depth range of these shallowly dipping thrust faults typically extends from 12 ± 2-km to 45 ± 9-km depth (Hayes et al, 2018), although some events involve rupture that extends up to the seafloor near the trench (~2 to 8 km below sea level).…”