The 2016 Mw 7.8 Pedernales, Ecuador, Earthquake: Rapid Response Deployment

Abstract

The April 2016, Pedernales Earthquake ruptured a 100 km by 40 km segment of the subduction zone along the coast of Ecuador in an Mw 7.8 megathrust event east of the intersection of the Carnegie Ridge with the trench. This portion of the subduction zone has ruptured on decadal time scales in similar size and larger earthquakes, and exhibits a range of slip behaviors, variations in segmentation, and degree of plate coupling along strike. Immediately after the earthquake, an international rapid response effort coordinated by the Instituto Geofísico at the Escuela Politécnica Nacional in Quito deployed 55 seismometers and 10 OBS above the rupture zone and adjacent areas to record aftershocks. In this article we describe the details of the US portion of the rapid response and present an earthquake catalog from May 2016-May 2017 produced using data recorded by these stations. Aftershocks focus in distinct clusters within and around the rupture area and match spatial patterns observed in long term seismicity. For the first two and a half months, aftershocks exhibit a relatively sharp cutoff to the north of the mainshock rupture. In early July an earthquake swarm occurred ~100 km to the northeast of the mainshock in the epicentral region of a Mw 7.8 earthquake in 1958. In December, an increase in seismicity occurred ~70 km to the northeast of the mainshock in the epicentral region of the 1906 earthquake. Data from the Pedernales earthquake and aftershock sequence recorded by permanent seismic and geodetic networks in Ecuador and the dense aftershock deployment provide an opportunity to examine the persistence of asperities for large to great earthquakes over multiple seismic cycles, the role of asperities and slow slip in subduction zone Meltzer et al., SRL Data Mine: Pedernales RAPID Deployment 3 megathrust rupture, and the relationship between locked and creeping parts of the subduction interface.

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

“…Seismicity in the Pedernales sequence matches patterns observed during the interseismic phase of the earthquake cycle, as well as maximum moment release and aftershock patterns of historic earthquakes (Figure ; Rolandone et al, , Meltzer et al, ; Agurto‐Detzel et al, ; León‐Ríos et al, ). A uniform earthquake catalog produced for seismic hazard assessment in Ecuador provides a basis for placing the Pedernales seismic sequence in the context of instrumental and historic seismicity from 1587 to 2009 (Beauval et al, ; Yepes et al, ).…”

“…A uniform earthquake catalog produced for seismic hazard assessment in Ecuador provides a basis for placing the Pedernales seismic sequence in the context of instrumental and historic seismicity from 1587 to 2009 (Beauval et al, 2013;Yepes et al, 2016). Similar patterns of focused clusters of seismicity are observed in both the background (interseismic) seismicity and postseismic Pedernales sequence (Figures 14a and 14b; Meltzer et al, 2019. The extent to which seismicity is more focused or diffuse is in part related to station density recording the postseismic sequence and in part due to the presence or absence of earthquake swarms during the period of observation (Figure 15).…”

“…The Pedernales seismic sequence is dominated by pronounced spatial clustering and a striking downdip limit in seismic activity. Most of the events locate outside the rupture area of the main shock (Figure ; Meltzer et al, ; Agurto‐Detzel et al, ; León‐Ríos et al, ). Three apparent bands of seismicity run perpendicular to the strike of the trench: the Jama band updip from the southern end of the rupture, the Cojimies‐Atacames Seamount band approximately coincident with the northern end of the rupture, and the Galera band approximately 20 km north of the rupture (Figure ).…”

“…A dense network of broadband, intermediate, and short‐period seismometers were installed between 9 and 22 May 2016, beginning 23 days after the mainshock (Figure S1 in the supporting information; Meltzer et al, ). These stations were in place for a year (into May 2017), with a small number of stations remaining in the field into July 2017.…”

“…In April 2016, the Mw 7.8 Pedernales, Ecuador, earthquake ruptured an approximately 100‐km × 40‐km segment of the subduction zone east and northeast of the intersection of the Carnegie ridge with the trench (Figure ). In the wake of the mainshock, an international rapid response effort coordinated by the Instituto Geofísico at the Escuela Politécnica Nacional (IGEPN) in Quito deployed a temporary network of seismometers along the North Ecuador subduction zone (Meltzer et al, ). These temporary stations densified coastal stations of the permanent national network (RENSIG; Alvarado et al, ).…”