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Abstract

Strong earthquakes cause transient perturbations of the near Earth’s surface system. These include the widespread landsliding and subsequent mass movement and the loading of rivers with sediments. In addition, rock mass is shattered during the event, forming cracks that affect rock strength and hydrological conductivity. Often overlooked in the immediate aftermath of an earthquake, these perturbations can represent a major part of the overall disaster with an impact that can last for years before restoring to background conditions. Thus, the relaxation phase is part of the seismically induced change by an earthquake and needs to be monitored in order to understand the full impact of earthquakes on the Earth system. Early June 2015, shortly after the April 2015 Mw7.9 Gorkha earthquake, we installed an array of 12 seismometers and geophones and 6 weather stations in the upper Bhotekoshi catchment, covering an area of ~50 km2. The seismic network was optimized for the monitoring of Earth surface processes (landsliding, mass wasting river processes, debris flows) and for the monitoring of properties of the shallow subsurface by coda analysis. To achieve the latter aim and to probe different scales and depths, seismometers were installed with inter-station distances from about 80m to 9km. In particular, in each of two locations close to the Bhotekoshi river, three seismometers were installed in small arrays with inter-station distances of about 100m. The seismic array is part of a wider data acquisition strategy including hydrometric measurements and high resolution optical (RapidEye) and radar imagery (TanDEM TerraSAR-X).