Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal.

This is the author accepted manuscript. The final version is available from AAAS via http://dx.doi.org/10.1126/science.aac6383Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015 moment magnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network. We used GPS and interferometric synthetic aperture radar data to model the earthquake rupture as a slip pulse ~20 kilometers in width, ~6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at ~3.3 kilometers per second over ~140 kilometers. The smooth slip onset, indicating a large (~5-meter) slip-weakening distance, caused moderate ground shaking at high frequencies (>1 hertz; peak ground acceleration, ~16% of Earth's gravity) and minimized damage to vernacular dwellings. Whole-basin resonance at a period of 4 to 5 seconds caused the collapse of tall structures, including cultural artifacts.The Nepal Geodetic Array was funded by internal funding to JPA from Caltech and DASE and by the Gordon and Betty Moore Foundation, through Grant GBMF 423.01 to the Caltech Tectonics Observatory and was maintained thanks to NSF Grant EAR 13-5136. Andrew Miner and the PAcific Northwest Geodetic Array (PANGA) at Central Washington University are thanked for technical assistance with the construction and operation of the Tribhuvan University-CWU network. Additional funding for the TU-CWU network came from United Nations Development Programme and Nepal Academy for Science and Technology. The high rate data were recovered thanks to a rapid intervention funded by NASA (US) and the Department of Foreign International Development (UK). We thank Trimble Navigation Ltd and the Vaidya family for supporting the rapid response as well. The accelerometer record at KATNP was provided by USGS. Research at UC Berkeley was funded by the Gordon and Betty Moore Foundation through grant GBMF 3024. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The GPS data were processed by ARIA (JPL) and the Scripps Orbit and Permanent Array Center. The effort at the Scripps Institution of Oceanography was funded by NASA grants NNX14AQ53G and NNX14AT33G. ALOS-2 data were provided under JAXA (Japan) PI Investigations 1148 and 1413. JPA thanks the Royal Society for support. We thank Susan Hough, Doug Given, Irving Flores and Jim Luetgert for contribution to the installation of this station

Topographic control of asynchronous glacial advances: A case study from Annapurna, Nepal

Differences in the timing of glacial advances, which are commonly attributed to climatic changes, can be due to variations in valley topography. Cosmogenic 10Be dates from 24 glacial moraine boulders in 5 valleys define two age populations, late-glacial and early Holocene. Moraine ages correlate with paleoglacier valley hypsometries. Moraines in valleys with lower maximum altitudes date to the late-glacial, whereas those in valleys with higher maximum altitudes are early Holocene. Two valleys with similar equilibrium-line altitudes (ELAs), but contrasting ages, are <5 km apart and share the same aspect, such that spatial differences in climate can be excluded. A glacial mass-balance cellular automata model of these two neighboring valleys predicts that change from a cooler-drier to warmer-wetter climate (as at the Holocene onset) would lead to the glacier in the higher altitude catchment advancing, while the lower one retreats or disappears, even though the ELA only shifted by ∼120 m. Copyright 2011 by the American Geophysical Union