
Descriptive Model of the July 17, 1998 Papua New Guinea Tsunami:
Assumptions and Specifications for Animations
Hydrodynamic Model:
 A linearized form of the shallowwater wave equations was used to simulate the tsunami. Because nonlinear terms were not included, the computations are probably only accurate for water depths deeper than 50 m.
 The computations were performed on a 3.7 km grid at a time interval of 10 seconds. Although the model is stable, the nearshore evolution of the tsunami is not accurately portrayed because of the large grid size.
 The model does not compute runup or inundation.
Earthquake Source Model:
 Because only the location, depth, and seismic moment of the event are known at this time, certain assumptions must be made to determine the rupture area and slip.
 Slip on the vertical plane is assumed.
 An empirical relationship is used to determine the rupture area from the seismic moment (Wells and Coppersmith, 1994). An assumed 3:2 aspect ratio (length:width) yields the dimensions of the rupture zone.
 Using the assumed rupture area (above) and a shear modulus of 30 GPa results in an average slip of 2.15 m.
 Assuming uniform slip typically underestimates the tsunami that is produced (Geist, 1998). Therefore, an arbitrary and symmetric slip distribution is assumed that averages to 2.15 m.
 Because this was a very shallow event, the rupture extends to the seafloor.
 A 10 second rise time is assumed, making this a nearly impulsive event with respect to tsunami propagation speeds.
 Because of the steep bathymetric gradient, errors in the epicenter location result in significant changes to the tsunami time history. The Harvard centroid location is used.
