M 7.9 - 140 km E of Kokopo, Papua New Guinea

  • 2016-12-17 10:51:10 (UTC)
  • 4.505°S 153.522°E
  • 94.5 km depth

Finite Fault

 Contributed by US last updated 2018-10-17 21:50:55 (UTC)
  • The data below are the most preferred data available
  • The data below have been reviewed by a scientist

Scientific Analysis

This is an update of an earlier, single-plane model. That prior model suggested shallow interface slip had been triggered by deeper intraplate faulting (where the event initiated). Here we model a two-plane solution, representing intraplate faulting at depth and shallow interface slip. We have tested a suite of models and favor this solution over other, similar, two-plane options, and more complex three-plane models that better represent the rotation in strike in the shallow subduction zone.

Data Process and Inversion

We analyzed 35 teleseismic broadband P waveforms, 4 broadband SH waveforms, and 0 long period surface waves selected based on data quality and azimuthal distribution. Waveforms are first converted to displacement by removing the instrument response and are then used to constrain the slip history using a finite fault inverse algorithm (Ji et al., 2002). We begin modeling using a hypocenter matching or adjusted slightly from the initial NEIC solution ( location = 4.5°S, 153.4°E; depth = 95.0 km ), and a fault plane defined using either the rapid W-Phase moment tensor (for near-real time solutions), or the gCMT moment tensor (for historic solutions).

Result

This result is based on the moment tensor nodal plane ( strike = 140.0°; dip = 48.0° ). The seismic moment release based upon this plane is 8.8e+20 N-m (Mw = 7.9) using a 1D crustal model interpolated from CRUST2.0 (Bassin et al., 2000).

This solution uses 2 plane segments (see Table below) designed to match a priori knowledge of the fault (e.g. 3D slab geometry).

Plane Segments
SegmentStrikeDip
1 140.0° 48.0°
2 320.0° 37.0°

Cross-section of Slip Distribution

Slip distribution map image
Cross-section of slip distribution. The strike direction is indicated above each fault plane and the hypocenter location is denoted by a star. Slip amplitude is shown in color and the motion direction of the hanging wall relative to the footwall (rake angle) is indicated with arrows. Contours show the rupture initiation time in seconds.

Surface Projection

Finite fault basemap
Surface projection of the slip distribution superimposed on GEBCO bathymetry. Thick white lines indicate major plate boundaries [Bird, 2003]. Gray circles, if present, are aftershock locations, sized by magnitude.

Moment Rate Function

Moment rate function image
Source time function, describing the rate of moment release with time after earthquake origin, relative to the peak moment rate (listed in the top right corner of the plot). The red dashed line represents the interpreted end of the event.