Paper summaries 2019

Abstract: The death toll and economic impact of an earthquake can be greatly exacerbated if seismic ground shaking triggers landslides. Earthquake-triggered landslides typically occur in two different contexts: localized failure of steep slopes and resulting landslides that pose a major threat to life in areas below; and lateral spreading of nearly flat sediment plains due to shaking-induced liquefaction, which can damage large areas of critical infrastructure. Unexpected catastrophic landsliding triggered by the 28 September 2018 earthquake at Palu, Indonesia did not occur in either typical context, but produced both destructive outcomes. Here, we show that alluvial ground failure in the Palu Valley was a direct consequence of irrigation creating a new liquefaction hazard. Aqueduct-supported cultivation, primarily of wet rice, raised the water table to near ground level, saturating sandy alluvial soils that liquefied in response to strong ground shaking. Large-displacement lateral spreads occurred on slopes of 1°. Slopes steeper than 1.5° sourced long-runout landslides and debris flows that swept through villages occupying the gentler slopes below. The resulting damage and loss of life would probably not have occurred in the absence of a raised water table. Earthquake-triggered landsliding of gentle, irrigated alluvial slopes is an under-recognized, but avoidable, anthropogenic hazard.

Abstract: The death toll and economic impact of an earthquake can be greatly exacerbated if seismic ground shaking triggers landslides. Earthquake-triggered landslides typically occur in two different contexts: localized failure of steep slopes and resulting landslides that pose a major threat to life in areas below; and lateral spreading of nearly flat sediment plains due to shaking-induced liquefaction, which can damage large areas of critical infrastructure. Unexpected catastrophic landsliding triggered by the 28 September 2018 earthquake at Palu, Indonesia did not occur in either typical context, but produced both destructive outcomes. Here, we show that alluvial ground failure in the Palu Valley was a direct consequence of irrigation creating a new liquefaction hazard. Aqueduct-supported cultivation, primarily of wet rice, raised the water table to near ground level, saturating sandy alluvial soils that liquefied in response to strong ground shaking. Large-displacement lateral spreads occurred on slopes of 1°. Slopes steeper than 1.5° sourced long-runout landslides and debris flows that swept through villages occupying the gentler slopes below. The resulting damage and loss of life would probably not have occurred in the absence of a raised water table. Earthquake-triggered landsliding of gentle, irrigated alluvial slopes is an under-recognized, but avoidable, anthropogenic hazard.

Abstract: Myanmar is located at the eastern margin of the ongoing Indo-Eurasian collision system, has experienced a complex tectonic history and is threatened by a high level of seismic hazard. Here we develop a crustal scale 3-D seismic velocity model of Myanmar, which is not only critical for understanding the regional tectonic setting and its evolution but can also provide the foundation for a variety of seismological studies, including earthquake location determinations, earthquake focal mechanism inversions, and ground motion simulations. We use the newly deployed Earth Observatory of Singapore-Myanmar broadband seismic network and other seismic stations in and around Myanmar to study the station-based 1-D velocity structure through a joint inversion of receiver functions, H/V amplitude ratio of Rayleigh waves, and surface wave dispersion measurements. Our results reveal a highly variable crustal structure across Myanmar region, characterized by a series of N-S trending sedimentary basins, with thicknesses up to ~15 km in central Myanmar and an ~5-km step in the depth of the Moho across the Sagaing-Shan Scarp fault system. We interpolate our station-based 1-D velocity profiles to obtain an integrated 3-D velocity model from southern Bangladesh to Myanmar. Using three regional earthquakes located to the south, within, and north of the seismic network, we show that our proposed model performs systematically better than the CRUST 1.0 model for both Pnl waves and surface waves. Our study provides a preliminary community velocity model for the region, with further refinements and interpretations anticipated in the near future.

Abstract: Myanmar is located at the eastern margin of the ongoing Indo-Eurasian collision system, has experienced a complex tectonic history and is threatened by a high level of seismic hazard. Here we develop a crustal scale 3-D seismic velocity model of Myanmar, which is not only critical for understanding the regional tectonic setting and its evolution but can also provide the foundation for a variety of seismological studies, including earthquake location determinations, earthquake focal mechanism inversions, and ground motion simulations. We use the newly deployed Earth Observatory of Singapore-Myanmar broadband seismic network and other seismic stations in and around Myanmar to study the station-based 1-D velocity structure through a joint inversion of receiver functions, H/V amplitude ratio of Rayleigh waves, and surface wave dispersion measurements. Our results reveal a highly variable crustal structure across Myanmar region, characterized by a series of N-S trending sedimentary basins, with thicknesses up to ~15 km in central Myanmar and an ~5-km step in the depth of the Moho across the Sagaing-Shan Scarp fault system. We interpolate our station-based 1-D velocity profiles to obtain an integrated 3-D velocity model from southern Bangladesh to Myanmar. Using three regional earthquakes located to the south, within, and north of the seismic network, we show that our proposed model performs systematically better than the CRUST 1.0 model for both Pnl waves and surface waves. Our study provides a preliminary community velocity model for the region, with further refinements and interpretations anticipated in the near future.