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

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Science  04 Sep 2015:
Vol. 349, Issue 6252, pp. 1091-1095
DOI: 10.1126/science.aac6383
  • Fig. 1 Cumulative slip distribution of and static stress drop due to the Gorkha earthquake.

    (A) Slip inversion results for the Mw 7.8 Gorkha event. The red star is the hypocenter. Dashed contours are depths to the fault. Orange diamonds are 5-Hz cGPS stations, and white diamonds are low-rate (1/30-Hz) stations. The green triangle is the strong-motion station. Kathmandu is represented by the blue square. The black arrows indicate the coseismic offsets measured at the sites (the values and uncertainties are given in table S1). Vectors with less than 10 cm of displacement are not shown. (B) Static stress drop predicted by the model of Fig. 1A. Green circles are aftershocks with local magnitudes greater than four, recorded and located by the Nepal National Seismic Center. Focal mechanisms (yellow and white circles) represent the global centroid-moment tensor solutions for aftershocks with magnitudes greater than six.

  • Fig. 2 Records of ground displacements and accelerations during the Gorkha earthquake.

    Shown are displacement waveforms at cGPS stations KKN4 and NAST (five samples per second) and acceleration waveforms at strong-motion station KATNP (Fig. 1).

  • Fig. 3 Evidence for resonance of the Kathmandu basin.

    (A to C) Three components of ground velocity observed at two high-rate GPS stations (KKN4 and NAST) and one strong-motion station (KATNP) in the Kathmandu region. KKN4 is located on hard rock northwest of Kathmandu, whereas the other two stations are located on soft sediment in the basin. The GPS is differentiated to velocity, and the strong-motion data are integrated after high-pass filtering at 0.02 Hz. (D to F) Ground-motion amplification observed at the two basin stations. Plotted is the ratio of the amplitude spectra of the basin stations to the amplitude spectra of the reference bedrock station, KKN4. (G to I) Five-percent damped velocity response spectra for all three stations. (J) Close-up map showing the location of the basin and bedrock stations.

  • Fig. 4 Slip-pulse kinematics during the Gorkha earthquake.

    (A) Snapshot of the slip rate on the MTH at 27 s after the origin time, during propagation of the seismic rupture from the model in Fig. 1. The red star is the hypocenter, and dashed contours represent the depth to the fault. The white circles are the centers of five subfaults used to compare against theoretical regularized Yoffe source time functions (28). (B) STFs at the five locations from (A). Plotted are the inverted slip rates and the regularized Yoffe functions measured from the vertical velocity at KKN4, scaled to the maximum observed slip rate at each point, which is indicated numerically. Time is relative to the hypocentral origin (28.147°N, 84.708°E; 25 April 2015, 06:11:26.270 UTC).

Supplementary Materials

  • Slip pulse and resonance of Kathmandu basin during the 2015 Mw 7.8 Gorkha earthquake, Nepal imaged with geodesy

    J. Galetzka, D. Melgar, J. F. Genrich, J. Geng, S. Owen, E. O. Lindsey, X. Xu, Y. Bock, J.-P. Avouac,* L. B. Adhikari, B. N. Upreti, B. Pratt-Sitaula, T. N. Bhattarai, B. P. Sitaula, A. Moore, K. W. Hudnut, W. Szeliga, J. Normandeau, M. Fend, M. Flouzat, L. Bollinger, P. Shrestha, B. Koirala, U. Gautam, M. Bhatterai, R. Gupta, T. Kandel, C. Timsina, S. N. Sapkota, S. Rajaure, N. Maharjan

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S11
    • Tables S1 and S2
    • Caption for Movies S1

    Images, Video, and Other Other Media

    Movie S1
    Animation showing the propagation of the slip-rate pulse derived from the joint inversion of the high-rate GPS, static GPS and InSAR data, compared with the timeevolution of the sources of high frequency (05-2Hz) teleseismic waves (5). The cumulative slip distribution from the model is shown in Figure 1C. Each frame shows the instantaneous slip rate of the source model. The red star is the hypocenter and dashed lines represent the depth to the fault.
    Correction (31 August 2015): In table S1, the displacement at station SNDL was reported erroneously. The correct displacement is: east, 0.047 ±0.002 m; north, �0.223 ±0.003 m; vertical, 0.003 ±0.003 m. The PDF has been corrected.
    The original version is accessible here.

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