“…Our models further reveal the feedback of shallow and deep segments as a frictional segmented system; that is, the influence of deep segment to shallow segment (Figure b) is stronger than the shallow segment to the deep segment (Figure a) in terms of failure time. This finding supports the hypothesis that the deep segment may influence the failure of the shallow segment (Bilham et al, ), which is applicable to subduction zones (e.g., Konca et al, ; Moreno et al, ).…”
Section: Discussionsupporting
confidence: 86%
“…These observations suggest that downdip seismogenic segmentation of the MHT is geometrically controlled (e.g., Qiu et al, ; Lindsey et al, ), as has been suggested in other regions (e.g., Bletery et al, ; Duan, ; Yang et al, ). However, slip distributions of the Gorkha earthquake mimic incomplete ruptures in other regions where incomplete rupture seem to be depth‐controlled, which is consitent with the notion that a plate boundary thrust is zoned according to frictional strength variations (e.g., Konca et al, ; Perfettini et al, ; Lay et al, ; Moreno et al, ). Previous numerical studies showed that depth‐varying friction may influence the earthquake size and timing (e.g., Gao & Wang, ; Moreno et al, ; Murphy et al, ).…”
Section: Introductionmentioning
confidence: 82%
“…Our models show that lower effective friction coefficients and/or higher dipping angles of deep segment would allow for diminished capacity to store shear stress within the seismogenic zone of a fault (Figure ), leading to an earlier failure time as would be expected from Coulomb failure (Figures b and b). This may explain why moderate‐size earthquakes (7 < M w < 8) tend to occur more frequently in the deeper portions of the seismogenic zone of the Himalayan arc (Bilham et al, ) as well as subduction zones (e.g., Moreno et al, ). The “geometrical stress deficit” may be particularly relevant here (Figure a).…”
Section: Discussionmentioning
confidence: 99%
“…Recent detailed earthquake studies highlight that there is a population of moderate‐ to large‐magnitude earthquakes ( M w > 7), termed zone‐C events (Lay et al, ), that rupture the deeper portions of plate boundary thrust faults in regions where larger ( M w 8–9+) earthquakes are known or suspected to have occurred (e.g., Barnhart et al, ; Beck et al, ; Bilham & England, ; Delouis et al, ; Elliott et al, ; Hayes et al, ; Iinuma et al, ; Konca et al, ; McNamara et al, ; Melgar et al, ; Moreno et al, ; Okada et al, ; Schurr et al, ; Simons et al, ). For example, the 2016 M w 7.6 Melinka, Chile earthquake partially ruptured a downdip portion of the 1960 M 9.5 Valdivia earthquake source region (Melgar et al, ; Moreno et al, ) and the 2015 M w 7.8 Gorkha, Nepal earthquake and its largest aftershock partially ruptured the Main Himalayan Thrust (MHT; e.g., Avouac et al, ; Elliott et al, ; Hayes et al, ; Mencin et al, ). These moderate‐magnitude events reflect incomplete ruptures of fault segments that later can rupture as great earthquakes, and the greater frequency of these moderate‐magnitude earthquakes lead to a heterogeneous strain distribution that may influence the timing and spatial distribution of subsequent earthquakes through the generation of an updip strain reservoir (e.g., Mencin et al, ).…”
Several recent moderate‐magnitude (Mw > 7) earthquakes, such as the 2015 Gorkha, Nepal, ruptured only the deep (>15 km depth) portions of megathrust faults, leaving the updip sections unbroken. Here we investigate the effects of geometrical and frictional variations at depth on the stress accumulation and release in ramp‐flat structures using 2‐D finite element models. Our results show that ramp‐flat structures allow for faster but lower shear stress accumulation with increasing dip of the deep ramp section while increasing frictional strength of the faults allows more stress accumulation. These factors lead to earlier yet smaller failures of the ramp followed by larger and less frequent failures affecting the shallow section. Our models thus suggest that the dynamics of strain reservoirs are related to both the frictional strength and dips of ramp‐flat megathrust structures, and the failure time of the shallow fault section is affected by the stress regime at the deep fault segment.
“…Our models further reveal the feedback of shallow and deep segments as a frictional segmented system; that is, the influence of deep segment to shallow segment (Figure b) is stronger than the shallow segment to the deep segment (Figure a) in terms of failure time. This finding supports the hypothesis that the deep segment may influence the failure of the shallow segment (Bilham et al, ), which is applicable to subduction zones (e.g., Konca et al, ; Moreno et al, ).…”
Section: Discussionsupporting
confidence: 86%
“…These observations suggest that downdip seismogenic segmentation of the MHT is geometrically controlled (e.g., Qiu et al, ; Lindsey et al, ), as has been suggested in other regions (e.g., Bletery et al, ; Duan, ; Yang et al, ). However, slip distributions of the Gorkha earthquake mimic incomplete ruptures in other regions where incomplete rupture seem to be depth‐controlled, which is consitent with the notion that a plate boundary thrust is zoned according to frictional strength variations (e.g., Konca et al, ; Perfettini et al, ; Lay et al, ; Moreno et al, ). Previous numerical studies showed that depth‐varying friction may influence the earthquake size and timing (e.g., Gao & Wang, ; Moreno et al, ; Murphy et al, ).…”
Section: Introductionmentioning
confidence: 82%
“…Our models show that lower effective friction coefficients and/or higher dipping angles of deep segment would allow for diminished capacity to store shear stress within the seismogenic zone of a fault (Figure ), leading to an earlier failure time as would be expected from Coulomb failure (Figures b and b). This may explain why moderate‐size earthquakes (7 < M w < 8) tend to occur more frequently in the deeper portions of the seismogenic zone of the Himalayan arc (Bilham et al, ) as well as subduction zones (e.g., Moreno et al, ). The “geometrical stress deficit” may be particularly relevant here (Figure a).…”
Section: Discussionmentioning
confidence: 99%
“…Recent detailed earthquake studies highlight that there is a population of moderate‐ to large‐magnitude earthquakes ( M w > 7), termed zone‐C events (Lay et al, ), that rupture the deeper portions of plate boundary thrust faults in regions where larger ( M w 8–9+) earthquakes are known or suspected to have occurred (e.g., Barnhart et al, ; Beck et al, ; Bilham & England, ; Delouis et al, ; Elliott et al, ; Hayes et al, ; Iinuma et al, ; Konca et al, ; McNamara et al, ; Melgar et al, ; Moreno et al, ; Okada et al, ; Schurr et al, ; Simons et al, ). For example, the 2016 M w 7.6 Melinka, Chile earthquake partially ruptured a downdip portion of the 1960 M 9.5 Valdivia earthquake source region (Melgar et al, ; Moreno et al, ) and the 2015 M w 7.8 Gorkha, Nepal earthquake and its largest aftershock partially ruptured the Main Himalayan Thrust (MHT; e.g., Avouac et al, ; Elliott et al, ; Hayes et al, ; Mencin et al, ). These moderate‐magnitude events reflect incomplete ruptures of fault segments that later can rupture as great earthquakes, and the greater frequency of these moderate‐magnitude earthquakes lead to a heterogeneous strain distribution that may influence the timing and spatial distribution of subsequent earthquakes through the generation of an updip strain reservoir (e.g., Mencin et al, ).…”
Several recent moderate‐magnitude (Mw > 7) earthquakes, such as the 2015 Gorkha, Nepal, ruptured only the deep (>15 km depth) portions of megathrust faults, leaving the updip sections unbroken. Here we investigate the effects of geometrical and frictional variations at depth on the stress accumulation and release in ramp‐flat structures using 2‐D finite element models. Our results show that ramp‐flat structures allow for faster but lower shear stress accumulation with increasing dip of the deep ramp section while increasing frictional strength of the faults allows more stress accumulation. These factors lead to earlier yet smaller failures of the ramp followed by larger and less frequent failures affecting the shallow section. Our models thus suggest that the dynamics of strain reservoirs are related to both the frictional strength and dips of ramp‐flat megathrust structures, and the failure time of the shallow fault section is affected by the stress regime at the deep fault segment.
“…The 2016 M w 7.6 earthquake, which broke a small patch of the deep seismogenic locked zone beneath Chiloé Island’s southern coast (Fig. 1b), announced the seismic reawakening of the 1960 rupture zone 30,31 . Regional interseismic plate locking estimated from horizontal components of 17 campaign and 6 continuous GPS stations suggest a high degree of locking below southern Chiloé and Guafo islands over a much larger region than the 2016 rupture zone 12,30 .Fig.…”
Great megathrust earthquakes arise from the sudden release of energy accumulated during centuries of interseismic plate convergence. The moment deficit (energy available for future earthquakes) is commonly inferred by integrating the rate of interseismic plate locking over the time since the previous great earthquake. But accurate integration requires knowledge of how interseismic plate locking changes decades after earthquakes, measurements not available for most great earthquakes. Here we reconstruct the post-earthquake history of plate locking at Guafo Island, above the seismogenic zone of the giant 1960 (Mw = 9.5) Chile earthquake, through forward modeling of land-level changes inferred from aerial imagery (since 1974) and measured by GPS (since 1994). We find that interseismic locking increased to ~70% in the decade following the 1960 earthquake and then gradually to 100% by 2005. Our findings illustrate the transient evolution of plate locking in Chile, and suggest a similarly complex evolution elsewhere, with implications for the time- and magnitude-dependent probability of future events.
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