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High-Impact Earthquakes on Hidden, Secondary Faults Within the Sparsely Instrumented Golden Triangle Region of Laos, Thailand, and Myanmar

Description: 

The Golden Triangle region of Laos, Thailand, and Myanmar (SE India-Eurasia collision zone) is crossed by >100 km-long, NE-striking sinistral faults, host to events of up to M_w 6.8 (2011 Tarlay). In the past decade, six M_w ≥5.5 events struck the area, providing new insights into its active tectonics. The largest of these, the 2019 M_w 6.2 Sainyabuli, Laos earthquake, struck 40 km from a major reservoir and 90 km from a UNESCO World Heritage Site, illustrating the need to reassess the earthquake potential of this area despite its modest background seismicity. In this study, we solved for source parameters of three M_w ≥5.5 events using Sentinel-1 InSAR. The Sainyabuli mainshock ruptured a previously unknown, 24 km-long, NNW-trending, dextral strike-slip fault with little topographic expression, with slip focused above 12 km but leaving a pronounced shallow slip deficit. InSAR modelling of the other two M_w ≥5.5 events also revealed rupture on NW-trending, ~10 km-long, unmapped faults. Collectively, this shows that the region contains conjugate faults long enough to generate damaging earthquakes but which are little evident in the topography. To understand the seismicity depth distribution and its implication for seismogenic thickness, we also relocated 198 well-recorded events between 1978–2022 using mloc software. We overcame the challenge of limited local-regional station coverage by incorporating seismic sequences from across a broad area into the relocation cluster. Since these events also share teleseismic station recordings, the collective local-regional coverage is improved. The calibrated catalog contains focal depths of 6–24 km, each with ±4 km uncertainties. The seismicity cut off thus extends far deeper than the Sainyabuli mainshock slip, potentially leaving an unruptured deeper fault as an ongoing hazard. Our combined geodetic and seismological approach shows that shorter, NW-oriented faults should be considered alongside the longer NE-trending faults in hazard models and earthquake scenarios. Our study also provides a blueprint for relocating earthquakes in other sparsely instrumented regions.

Session: Research Advances in “High-Impact”, “Under-Studied” Earthquakes and Their Impacts on Communities [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Israporn

Student Presenter: Yes

Invited Presentation: 

Authors