Nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface

Abstract

The Nicoya Peninsula in Costa Rica is one of the few places on Earth where the seismically active plate interface of a subduction zone is directly overlaid by land rather than ocean. At this plate interface, large megathrust earthquakes with magnitudes greater than 7 occur approximately every 50 years. Such quakes occurred in 1853, 1900 and 1950, so another large earthquake had been anticipated 1,2 . Land-based Global Positioning System 3,4 (GPS) and seismic 5-7 measurements revealed a region where the plate interface was locked and hence accumulated seismic strain that could be released in future earthquakes. On 5 September 2012, the longanticipated Nicoya earthquake occurred in the heart of the previously identified locked patch. Here we report observations of coseismic deformation from GPS and geomorphic data along the Nicoya Peninsula and show that the magnitude 7.6 Nicoya earthquake ruptured the lateral and down-dip extent of the previously locked region of the plate interface. We also identify a previously locked part of the plate interface, located immediately offshore, that may not have slipped during the 2012 earthquake, where monitoring should continue. By pairing observations of the spatial extent of interseismic locking and subsequent coseismic rupture, we demonstrate the use of detailed near-field geodetic investigations during the late interseismic period for identifying future earthquake potential.The interface between convergent plates produces most of the world's largest earthquakes, threatening local inhabitants and global populations through destructive shaking and tsunami generation, as demonstrated by the recent 2011 M w 9.0 Tohoku-Oki and 2004 M w 9.15 Sumatra-Andaman earthquakes and tsunami. Owing to the significant societal impacts, geoscientists endeavour to understand the driving and locking mechanisms controlling subduction zone seismicity. The shallow earthquakegenerating portion of the subduction interface, hereafter referred to as the megathrust, is difficult to characterize because it is relatively inaccessible, spans great lengths of continental margins and requires detailed near-field observations primarily in the marine environment.

Subduction zone megathrust earthquakes

“…For example, geodetic and paleogeodetic observations dating back several decades suggest heterogeneous patterns of strong coupling along the Sumatra margin, and the strongly coupled zones served as the highslip regions in the 2005 M w 8.7 Nias, and 2007 M w 8.4 and M w 7.9 Sumatra earthquakes (Chlieh et al, 2008). Similar observations of strong locking found in regions of high coseismic slip exist for the 2007 M w 8.0 Pisco, Peru , 2010 M w 8.8 Maule, Chile , 2011 M w 9 Tohoku (e.g., Ozawa et al, 2012), 2012 M w 7.8 Nicoya, Costa Rica (e.g., Protti et al, 2014), and the 2016 M w 7.8 Ecuador (Ye et al, 2016a) earthquakes.…”

Scenario Source Models and Strong Ground Motion for Future Mega‐earthquakes: Application to Lima, Central Peru

“…In addition, the 2012 megathrust earthquake below the Nicoya Peninsula in Costa Rica (M w 7.6) also occurred in the heart of a previously identified locked patch of the Cocos-Caribbean plate interface (Protti et al, 2013), providing strong supporting evidence for the coincidence of coseismic slip and high interseismic coupling areas. This earthquake was unique in that it ruptured a region at the Cocos-Caribbean plate interface where the subduction zone is overlaid by the Peninsula and was densely instrumented before the earthquake, allowing a high spatial resolution image of the plate coupling and coseismic slip (Protti et al, 2013). However, in general, resolution of plate coupling distribution as well as slip models of earthquakes in subduction regions is limited because they are typically based on land measurements away from the trench axis of seismogenic zones, making estimation of shallow coupling very difficult.…”

“…On the other hand there are many other examples of coincidence between coseismic slip and interseismic coupling for worldwide subduction zones such as in Sumatra Konca et al, 2008), in Japan (Hashimoto et al, 2009;Loveless and Meade, 2011), and in Chile (Moreno et al, 2010). In addition, the 2012 megathrust earthquake below the Nicoya Peninsula in Costa Rica (M w 7.6) also occurred in the heart of a previously identified locked patch of the Cocos-Caribbean plate interface (Protti et al, 2013), providing strong supporting evidence for the coincidence of coseismic slip and high interseismic coupling areas. This earthquake was unique in that it ruptured a region at the Cocos-Caribbean plate interface where the subduction zone is overlaid by the Peninsula and was densely instrumented before the earthquake, allowing a high spatial resolution image of the plate coupling and coseismic slip (Protti et al, 2013).…”

Earthquake and tsunami forecasts: Relation of slow slip events to subsequent earthquake rupture

“…Of course, we do not know if such behavior will continue in the future. Prior events in 1900 and 1950 appear to have ruptured approximately the same patch (1,19). The better located 1978 event (Mw 6.9) was smaller than the 2012 event (Mw 7.6) but also ruptured in the same area.…”