Coseismic Slip Deficit of the 2017 Mw 6.5 Ormoc Earthquake That Occurred Along a Creeping Segment and Geothermal Field of the Philippine Fault

Abstract

Coseismic surface deformation imaged through interferometric synthetic aperture radar (InSAR) measurements was used to estimate the fault geometry and slip distribution of the 2017 Mw 6.5 Ormoc earthquake along a creeping segment of the Philippine Fault on Leyte Island. Our best fitting faulting model suggests that the coseismic rupture occurred on a fault plane with high dip angle of 78.5° and strike angle of 325.8°, and the estimated maximum fault slip of 2.3 m is located at 6.5 km east‐northeast of the town of Kananga. The recognized insignificant slip in the Tongonan geothermal field zone implies that the plastic behavior caused by high geothermal gradient underneath the Tongonan geothermal field could prevent the coseismic failure in heated rock mass in this zone. The predicted Coulomb failure stress change shows that a significant positive Coulomb failure stress change occurred along the SE segment of central Philippine Fault with insignificant coseismic slip and infrequent aftershocks, which suggests an increasing risk for future seismic hazard.

Surface creep rate distribution along the Philippine fault, Leyte Island, and possible repeating of Mw ~ 6.5 earthquakes on an isolated locked patch

“…On 6 July 2017, an M w 6.5 ( M s 6.5) earthquake struck the northern area of Leyte (Fig. 2, Table 1), close to the town of Ormoc (Yang et al 2018). One of the nodal planes of its focal mechanism determined by the U.S. Geological Survey (USGS) is consistent with a rupture of the Philippine fault, with mainly NW striking left-lateral slip.…”

“…One of the nodal planes of its focal mechanism determined by the U.S. Geological Survey (USGS) is consistent with a rupture of the Philippine fault, with mainly NW striking left-lateral slip. Yang et al (2018) obtained coseismic displacements of the 2017 earthquake from InSAR analyses of ALOS-2 and Sentinel-1A satellite data. They used the displacements measured by InSAR to infer the fault geometry and coseismic slip distribution of the earthquake.…”

“…For the purpose of estimating the fault slip distribution of the 6 July 2017 earthquake, we used the ascending and descending ALOS-2/PALSAR-2 images, both obtained with right-looking mode, used in a previous study (Yang et al 2018). Our main emphasis was put on comparing the extent and amount of the fault slip of the 2017 earthquake with what we obtained in the coupling and creep analysis described in the previous section.…”

Structural Controls on Rupture Extent of Recent Sumatran Fault Zone Earthquakes, Indonesia

“…This part of the SFZ is characterized by intense geothermal activity ( Figure 5) (Hochstein & Sudarman, 2008;JICA, 1989) and high temperatures (above~200°C) at a depth of 1-2 km (JICA, 1989;Prastika et al, 2016;Silitonga et al, 2015). The relative absence of deep slip during the Dikit rupture ( Figure 7) may reflect a shallower maximum seismogenic depth associated with this high geothermal gradient (Yang et al, 2018), and an even higher heat flux in the area of the magmatic step over could have prevented northward continuation of the rupture. Such local relationships between structural step overs, volcanic centers, and earthquakes may be particularly important for the arc-related SFZ.…”

Co-Seismic and Postseismic Fault Models of the 2018 Mw 6.4 Hualien Earthquake Occurred in the Junction of Collision and Subduction Boundaries Offshore Eastern Taiwan

“…To get the global best fitting parameters, one hundred times above searching processes with random and individual starting values are performed. Finally, we re-divide the fault planes using the small size of 2 km × 2 km along the strike and down-dip directions to obtain the fine slip distribution of the 2018 Hualien earthquake, the same process for studying the co-seismic slip deficit of the 2017 Mw 6.5 Ormoc earthquake [26]. The fault planes are firstly divided using the large size of 5 km × 5 km along the strike and down-dip directions.…”