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The Relationship Between Seismic and Aseismic Slip on the Creeping Segment of the Philippine Fault: Insight to Earthquake Recurrence and Fault Mechanics

Shallow creep on the Leyte island section of the Philippine Fault was first estimated with campaign GPS data in the early 1990s. With the occurrence of a significant moment magnitude (M_w) 6.5 earthquake in July 2017 in northern Leyte, exploring the variability of the slip mode and the seismogenic potential of the “creeping segment” is important for furthering our understanding of fault mechanics and seismic hazard.

We present the first distributed interseismic slip model of the Philippine Fault, along ~100 km of the mappable trace on Leyte island. We make a direct comparison of the interseismic slip distribution (from ALOS InSAR time-series) to the coseismic slip (from Sentinel-1 and ALOS-2 interferograms), with models derived in a Bayesian framework.

Assuming a linear velocity between 2007-2011, we find fast aseismic slip rates throughout most of the fault across the seismogenic zone, around the 3.3 ± 0.2 cm/yr secular slip rate. The only exception is an area of significant slip deficit on a 20-km long, 7-km deep segment in the middle of the fault (the ‘Tongonan Segment’). Our coseismic models of the July 2017 M_w 6.5 mainshock and a M_w 5.8 aftershock suggest that the extent of seismic slip was largely complementary to the interseismic distribution, hence suggesting that the Tongonan segment is a seismogenic asperity. The time between a similar earthquake in 1947 falls within the 95% probability range of the earthquake return period based on a moment budget analysis from the slip models. Geological factors, such as the abundance of fluids from the active hydrothermal systems along the fault, as well as the presence of rate-weakening minerals, may provide conditions suitable for the aseismic slip on the fault.

Presenting Author: John Dale B. Dianala

Student Presenter: Yes

Day: 4/20/2021

Time: 5:30 PM - 6:45 PM Pacific

Additional Authors