|Title||Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||Galetzka J., Melgar D, Genrich J.F, Geng J., Owen S., Lindsey EO, Xu X., Bock Y, Avouac J.P, Adhikari L.B, Upreti B.N, Pratt-Sitaula B., Bhattarai T.N, Sitaula B.P, Moore A., Hudnut K.W, Szeliga W., Normandeau J., Fend M., Flouzat M., Bollinger L., Shrestha P., Koirala B., Gautam U., Bhatterai M., Gupta R., Kandel T., Timsina C., Sapkota S.N, Rajaure S., Maharjan N.|
|Type of Article||Article|
|Keywords||faults; friction laws; GPS; ground-motion; himalaya; inversion; rupture; strong-motion; time|
Detailed 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 similar to 20 kilometers in width, similar to 6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at similar to 3.3 kilometers per second over similar to 140 kilometers. The smooth slip onset, indicating a large (similar to 5-meter) slip-weakening distance, caused moderate ground shaking at high frequencies (>1 hertz; peak ground acceleration, similar to 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.
Our study provides insight into the main factors that determined the damage sustained during the Gorkha earthquake. Although the hypocenter was ~80 km away from the city, the main asperity that radiated most of the energy was much closer, just north of the basin and at a relatively shallow depth... Kathmandu was faced with a combination of source and site effects. The rupture directivity focused radiated seismic energy toward the city; the smooth onset and 6- to 7-s duration of the pulse excited a resonance of the Kathmandu basin, producing a protracted duration of violent shaking at a period of around 4 s.