Landslide Hazard in Aizawl, India Revealed from Field and Geodetic Observations and Hillslope Stability Analysis

Abstract:

Aizawl, the capital city of Mizoram, India, is highly susceptible to deep-seated landslides. Weak and porous shale and sandstone bedrock, high levels of precipitation during the monsoon season, steep hillslopes, and unregulated development contribute to this problem. M > 7 earthquakes along megathrusts beneath the Burma Fold Belt could trigger over 1,100 landslides and endanger over 300,000 people, increasing the severity of the landslide risk. In this study, we surveyed two slides in the south and east parts of Aizawl and from crack orientations we have inferred ground motion and created vector maps of the two slides. A shallow slope stability analysis (SHALSTAB) for the Aizawl area enabled us to map zones of relative hazard in Aizawl and the vicinity. Our SHALSTAB analysis suggests that 44% of our study area in Aizawl is unconditionally unstable. Similarly, preliminary results from a Newmark Deformation Analysis indicate that nearly 50% of our study area would result in landslide-inducing displacement under seismic loading from a magnitude 7 event. Both results indicate unconditionally unstable conditions in the south and east sides of Aizawl, which agree with our field investigation. We are analyzing Interferometry synthetic aperture radar (InSAR) data collected between 1998 and 2010 that we hope will demonstrate a seasonal time series of slope deformation for the region and determine slide velocities. With data from the Tropical Rainfall Measuring Mission (TRMM) we expect to confirm a correlation between slope movement and landslide occurrence with seasonal and annual precipitation.