Updated concepts of seismic gaps and asperities to assess great earthquake hazard along South America

Abstract

So far in this century, six very large–magnitude earthquakes ( M W ≥ 7.8) have ruptured separate portions of the subduction zone plate boundary of western South America along Ecuador, Peru, and Chile. Each source region had last experienced a very large earthquake from 74 to 261 y earlier. This history led to their designation in advance as seismic gaps with potential to host future large earthquakes. Deployments of geodetic and seismic monitoring instruments in several of the seismic gaps enhanced resolution of the subsequent faulting processes, revealing preevent patterns of geodetic slip deficit accumulation and heterogeneous coseismic slip on the megathrust fault. Localized regions of large slip, or asperities, appear to have influenced variability in how each source region ruptured relative to prior events, as repeated ruptures have had similar, but not identical slip distributions. We consider updated perspectives of seismic gaps, asperities, and geodetic locking to assess current very large earthquake hazard along the South American subduction zone, noting regions of particular concern in northern Ecuador and Colombia (1958/1906 rupture zone), southeastern Peru (southeasternmost 1868 rupture zone), north Chile (1877 rupture zone), and north-central Chile (1922 rupture zone) that have large geodetic slip deficit measurements and long intervals (from 64 to 154 y) since prior large events have struck those regions. Expanded geophysical measurements onshore and offshore in these seismic gaps may provide critical information about the strain cycle and fault stress buildup late in the seismic cycle in advance of the future great earthquakes that will eventually strike each region.

Upper Plate Faults May Contribute to the Paleoseismic Subsidence Record Along the Central Hikurangi Subduction Zone, Aotearoa New Zealand

“…There have been no large subduction earthquakes along the Hikurangi margin in historical times that could guide expected patterns of coastal deformation. At many subduction zones, the spatial pattern of coupled or partially coupled segments corresponds to slip patches in past great earthquakes (e.g., Chlieh et al., 2008; Loveless & Meade, 2011; Perfettini et al., 2010) and therefore persistent coupling may inform future earthquake behavior (e.g., Chlieh et al., 2011; Kaneko et al., 2010; Lay & Nishenko, 2022; Uchida & Bürgmann, 2021; L. Wang et al., 2015). Geodetic observations suggest predominantly low modern coupling on the central Hikurangi subduction zone, meaning convergence is currently accommodated through slow‐slip and creep (Wallace et al., 2004; Woods, 2022).…”

An Updated Fault Coupling Model Along Major Block‐Bounding Faults on the Eastern and Northeastern Tibetan Plateau From a Stress‐Constrained Inversion of GPS and InSAR Data

“…However, the slip deficit rates between 0 and 1 are spatial but also temporal average of creep that surrounds numerous small locked asperities (Wallace et al., 2004). “Asperities” are fault parts with full frictionally locking and exhibiting notable volumetric strain release in large coseismic slip, recognized in increasingly well‐constrained finite‐fault slip models worldwide (e.g., Lay & Nishenko, 2022). Frictionally locked asperities are likely to have high kinematic coupling or slip rate deficit, but a frictionally unlocked fault may have either high or low kinematic coupling due to the stress shadow effect imparted by nearby frictionally locked asperities (Lindsey et al., 2021; Wang & Bilek, 2014).…”

“…Factors controlling coupling include effective stress and frictional properties on the fault and their combination (e.g., Moore & Rymer, 2007). Thus, the heterogeneous pattern of fault coupling may result from the heterogeneous nature of the geophysical properties of the rocks that make up the faults and the fault geometry (Lay & Nishenko, 2022; Y. K. Liu et al., 2022). The vast region of the eastern and northern Tibetan plateau displays crustal deformation at various spatial scales and within distinct tectonic regimes, such as the transpression‐dominated Longmenshan fault and the shear‐dominated Kunlun fault (Wang & Shen, 2020; Zhang et al., 2004; Zuza & Yin, 2016).…”

“…The vast region of the eastern and northern Tibetan plateau displays crustal deformation at various spatial scales and within distinct tectonic regimes, such as the transpression‐dominated Longmenshan fault and the shear‐dominated Kunlun fault (Wang & Shen, 2020; Zhang et al., 2004; Zuza & Yin, 2016). In addition, the regional spatiotemporal variation of lithology, hydrologic conditions, and earthquake history may result in a heterogeneous pattern of fault coupling distribution at a local scale (Li & Bürgmann, 2021; Lay & Nishenko, 2022; J. Liu et al., 2022).…”

Construction of Long-term Seismic Catalog with Deep Learning and Characterization of Preseismic Fault Behavior in the Ridgecrest-Coso Region (2008-2019)

“…However, a huge portion of faults generate low seismicity rate during the interseismic period because of a high locking ratio (e.g. Bletery et al, 2020;Chamberlain et al, 2021;Uchida and Bürgmann, 2021;Zhou et al, 2022b), and these faults are manuscript submitted to Geophysical Research Letters also prone to large earthquakes (Sykes, 2021;Lay and Nishenko, 2022). To study the strongly locked faults, a long-term observation is always necessary.…”