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Source study of the 1996 MW 8.2 Biak (Papua, Indonesia) earthquake: relations to regional tectonics and directivity effect


The northern region of Cenderawasih Bay is a subduction zone segment of the Micro-Caroline Ocean plate with the Australian Continental Plate. Some tsunamigenic earthquakes had been recorded here in 1914 and 1996; however, the source characteristics and seismogenesis are not well investigated. In this study, we perform earthquake source modeling and directivity analysis. A finite fault model is obtained to determine the asperity location through body-wave inversion. This study found a distinct segment on the southern part of the subduction that ruptured the 1996 earthquake and extending westward and might be related to the rupture of the previous earthquake. The directivity effect can be seen from the amplitude and the time it takes to reach the highest amplitude (Tr) relative to the P-wave’s arrival time (P0). The vertical component’s directivity is affected by source propagation, whose direction depends on the rake. Besides, the radiation pattern also affects the directivity. On the other hand, the SH component has the largest energy emission direction on the side with the direction and opposite to the strike to show the fault plane’s orientation. We demonstrate that the upward-dip source mechanism in the Biak earthquake showing the directivity effect is different from the other mechanism, such as the strike-slip earthquake.

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Fig. 2

Source model of the 1996 Biak earthquake inverted in this study. a Final source-time-function. b Fix focal mechanism with strike 103°, dip 11°, and rake 69°. The final centroid depth is at 13.7 km. c Obtained slip distribution on the fault rupture plane. The black arrows indicate the slip vector on each grid. For the slip amplitudes and its surface projection, see Fig. 4

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We thank the Integrated Research Institute for Seismology (IRIS), Global Centroid-Moment-Tensor (Global CMT), and the United States Geology Survey (USGS) for providing data, initial parameter information, and open-source software (rdseed and Seismic Analysis Code). We use the Generic Mapping Tools (GMT) to produce figures. The program used in this study can be downloaded on the website The waveform used was obtained from IRIS Wilber3. The stations used are broadband stations on the GEOSCOPE (G), GSN-IRIS/USGS (IU), and GSN- IRIS/IDA (II) network. We thank the Editor and reviewers for comments and suggestions to improve the quality of this paper.

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Correspondence to Dimas Sianipar.

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The authors declare that they have no competing interests.

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Communicated by Longjun Dong.

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Arimuko, A., Sianipar, D. Source study of the 1996 MW 8.2 Biak (Papua, Indonesia) earthquake: relations to regional tectonics and directivity effect. Arab J Geosci 14, 2151 (2021).

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  • Finite fault
  • Asperity
  • Seismotectonic
  • Directivity
  • Radiation pattern