Seismicity Controlled by a Frictional Afterslip During a Small‐Magnitude Seismic Sequence (M_L < 5) on the Chihshang Fault, Taiwan

Abstract

We report evidence for frictional afterslip at shallow depths (about 5 to 7 km) during a small‐magnitude seismic sequence (with ML<5) along the Chihshang Fault, a main active structure of the Longitudinal Valley, in southeast Taiwan. The afterslip, which was recorded by a nearby borehole dilatometer, lasted about a month with a cumulative geodetic moment magnitude of 4.8 ± 0.2. The afterslip comprised two stages and controlled the aftershock sequence. The first postseismic stage, which followed a ML 4.6 earthquake, lasted about 6 h and mostly controlled the ruptures of neighboring asperities (e.g., multiplets) near the hypocenter. Then, a 4 week duration large afterslip event following a ML 4.9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep. The study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5. Furthermore, the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence.

Afterslip Enhanced Aftershock Activity During the 2017 Earthquake Sequence Near Sulphur Peak, Idaho

“…Although no GPS or strain meter data are available to test this idea directly, the 2017 Sulphur Peak aftershock migration rates are similar to those of other seismic sequences with confirmed afterslip (e.g., Canitano et al, 2018), as well as creep events in California (e.g., Linde et al, 1996;Lohman & McGuire, 2007). The combination of afterslip in the 2017 Sulphur Peak sequence and the cyclic/repeating nature of seismicity in this area-as indicated by the previous energetic, co-located sequences in 1960 and 1982-suggests that southeastern Idaho might be a region with slow-slip or creep (Peng & Gomberg, 2010), a style of deformation that is consistent with the relatively high strain rates (Payne et al, 2012;Schmeelk et al, 2017) and high heat flow (Blackwell et al, 2011) in the region.…”

Testing the Influence of Static and Dynamic Stress Perturbations On the Occurrence of a Shallow, Slow Slip Event in Eastern Taiwan

“…The SSE occurred at the depth of ∼2 to 4 km in the Ruisui region, possibly at the transition between the aseismic section of the LVF or CRF and the locked zone. This new evidence for aseismic slip detection by borehole strainmeters complement the detection of shallow postseismic slip (with M ∼ 4.8 ± 0.2) on the southern section of the LVF (Canitano, Godano, et al, ). Aseismic slip can occur at shallow depths due to the low temperature and pressure conditions (e.g., Marone et al, ; Peng & Gomberg, ).…”

“…It has produced moderate to large earthquakes, which includes the 1951 M L 7.3 Taitung earthquake (Chen et al, ) and the 2003 M w 6.8 Chengkung earthquake (Ching et al, ). The fault also displays aseismic slip at seismogenic depths, as evidenced by moderate to large frictional afterslip (Canitano, Godano, et al, ; Y. J. Hsu et al, ). Based on the analysis of 18 years of geodetic data (1992–2010) for the LVF which includes the large postseismic slip following the 2003 Chengkung earthquake (e.g., Y. J. Hsu et al, ), M. Y. Thomas et al () inferred that a major fraction (>80%) of the long‐term slip budget on the southern section of the LVF is the result of aseismic slip.…”

“…It has produced moderate to large earthquakes, which includes the 1951 M L 7.3 Taitung earthquake (Chen et al, 2008) and the 2003 M w 6.8 Chengkung earthquake (Ching et al, 2007). The fault also displays aseismic slip at seismogenic depths, as evidenced by moderate to large frictional afterslip (Canitano, Godano, et al, 2018; Y. J. Hsu et al, 2009).…”

Fault Heterogeneity and the Connection between Aftershocks and Afterslip

“…and known as the Omori law. The proportionality between aftershock occurrence rate, λ(t), and stress or strain rate,u(t), has been documented by the postseismic deformation measured after several large earthquakes [3,10,[21][22][23][24][25][27][28][29]. Perfettini and Avouac [23] explained the observed proportionality under the assumption that aftershocks are induced by afterslip.…”