THOR Projects for 2017
Seismic hazard assessment of the Kathmandu basin via nonlinear ground motion, earthquake cycle and rupture simulations (continuation)
On April 25, 2015, Nepal was hit by the magnitude 7.8 Gorkha earthquake. Contrary to the expected devastation for such a large magnitude event in a region with such poor construction practice, the observed structural damage, ground failure effects (e.g. landslides and liquefaction) and recorded ground motions showed only moderate shaking intensities throughout most of the near-field region. The death toll, while very high, was orders of magnitude lower than the number of casualties caused by similar magnitude earthquakes in regions with comparable infrastructure. The few isolated incidences of severe damage were generally associated with topographic amplification along ridge tops or with topography and basin edge effects at the outskirts of Kathmandu. The fact that the Gorkha earthquake was not nearly as devastating as we originally feared, raises nonetheless numerous urgent questions at the interface between earthquake engineering and basic earthquake research that this project addresses.
Dispersion of a natural hazard: ash clouds
Exploring the potential for glacier monitoring with seismic noise interferometry
Glaciers pose hazards at both short and long time scales. Glacial lake outburst floods (GLOFs) and glacial avalanches/surges can cause severe damage to human and infrastructures in large areas within minutes to hours. The most deadly glacier disaster, the 1970 glacier avalanche from Mount Huascarán in Peru, killed more than 6000 people in the town Yungay. At long time scales (years to decades), glaciers respond to climate change, cause global sea level change, and influence availability of water resources. For example, nearly a billion people in Bhutan, Nepal, China, and Indian rely heavily on meltwater from Himalayan glaciers for hydropower generation, agriculture, and ecosystems. Furthermore, the two time scales are linked: recent evidences show that global warming appears to enhance the short time scale hazards, such as GLOFs and surges in high-mountain areas (Bolch et al., 2012).
In this proposal, we will focus on glacial movements at short time scales, such as surges and avalanches. The physical causes behind these sudden glacier movements are still unclear, which makes them difficult to predict/forecast. Numerous evidences show that they probably involve changes in glacier basal conditions. In the seminal 1987 paper, Kamb proposed that glacial surge is due to switch of basal water system from concentrated large tunnels to a distributed "layer" as "connected cavities". The higher water pressure in the distributed system reduces friction and causes accelerations in ice flow. Unfortunately, this hypothesis has not been fully tested due to spatially and temporally limited data about glacial basal conditions (Tsai et al., 2016).
Therefore, to understand the physical mechanism behind rapid glacial sliding, and mitigate related glacial hazards, we need to develop new methods to complement existing methods (e.g., remote sensing, GPS, borehole measurements) so as to provide continuous monitoring of the glacial sliding interface, especially the distribution of water on the interface.