Structural Control on Megathrust Rupture and Slip Behavior: Insights From the 2016 Mw 7.8 Pedernales Ecuador Earthquake

Abstract

The heterogeneous seafloor topography of the Nazca Plate as it enters the Ecuador subduction zone provides an opportunity to document the influence of seafloor roughness on slip behavior and megathrust rupture. The 2016 Mw 7.8 Pedernales Ecuador earthquake was followed by a rich and active postseismic sequence. An internationally coordinated rapid response effort installed a temporary seismic network to densify coastal stations of the permanent Ecuadorian national seismic network. A combination of 82 onshore short and intermediate period and broadband seismic stations and six ocean bottom seismometers recorded the postseismic Pedernales sequence for over a year after the mainshock. A robust earthquake catalog combined with calibrated relocations for a subset of magnitude ≥4 earthquakes shows pronounced spatial and temporal clustering. A range of slip behavior accommodates postseismic deformation including earthquakes, slow slip events, and earthquake swarms. Models of plate coupling and the consistency of earthquake clustering and slip behavior through multiple seismic cycles reveal a segmented subduction zone primarily controlled by subducted seafloor topography, accreted terranes, and inherited structure. The 2016 Pedernales mainshock triggered moderate to strong earthquakes (5 ≤ M ≤ 7) and earthquake swarms north of the mainshock rupture close to the epicenter of the 1906 Mw 8.8 earthquake and in the segment of the subduction zone that ruptured in 1958 in a Mw 7.7 earthquake.

Rupture Process of the 2020 Mw7.0 Samos Earthquake and its Effect on Surrounding Active Faults

“…This is implied by the comparison of the coseismic slip distribution with the aftershock distribution (Figures 1a and 1d), where it is demonstrated that aftershocks cluster around the main slip patch and only very few aftershocks overlap the area of high coseismic slip. This remark is in line with other cases of individual moderate and large earthquakes, where the main asperities that broke during the main shock displayed low aftershock activity (e.g., Ebel & Chambers, 2016;Frank et al, 2017;Kato & Igarashi, 2012;Ross et al, 2017;Soto-Cordero et al, 2020;Zhang et al, 2021).…”

3D Local Earthquake Tomography of the Ecuadorian Margin in the Source Area of the 2016 Mw 7.8 Pedernales Earthquake

“…(2019), and Soto‐Cordero et al. (2020) but also at shallower depths (<20 km) in the upper crust as discussed by León‐Ríos et al. (2019) and Hoskins et al.…”

“…Quaternary sediments cover these as well as other small formations, forming several basins along the coast such as the Borbon, Manta–Jama, and Manabi basin (see (1), (2), and (3) in Figure 1b). The local tectonic and seismic activity is controlled by major faults that bound these basins (Agurto‐Detzel et al., 2019; Font et al., 2013; León‐Ríos et al., 2019; Luzieux et al., 2006; Reyes & Michaud, 2012; Reynaud et al., 1999; Soto‐Cordero et al., 2020). Reyes and Michaud (2012) updated the coastal geological map for Ecuador extending several faults observed at the surface.…”

Microseismicity appears to outline highly coupled regions on the Central Chile megathrust

“…The large acceleration of aseismic processes in the postseismic stage (Perfettini et al, 2010) then evokes a higher rate of microseismicity in these mostly creeping regions, which allows the clear identification of such separators close to the main shock area during aftershock series. A recent example is the area of the 2016 M w 7.8 Pedernales earthquake, where the main shock that was situated on the deeper part of the megathrust activated three narrow seismicity "fingers" separating largely aseismic regions in the presumably unruptured part of the megathrust (Agurto-Detzel et al, 2019;Soto-Cordero et al, 2020). As in Central Chile, these features can be correlated with incoming seafloor relief.…”