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Preliminary Numerical Simulation on the local tsunami generated

by November 16 2008 Sulawesi Earthquake

Xiaoming Wang, Gegar Prasetya and William Power

GNS Science, 1 Fairway drive, Avalon, Lower Hutt 5010, New Zealand

An earthquake of magnitude Mw7.6 stroke north Sulawesi, Indonesia at 01:02:31 on November 17, 2008

(local time). 50 houses were damaged, only a few people were injured and no casualties were reported. A small

local tsunami was also observed according to local residents. A numerical simulation was carried out shortly

after the earthquake. Numerical simulation shows that up to 30 cm tsunami was generated along the north

coast of Gorontalo (north Sulawesi Island). This is confirmed by information from Danny Hilman Natawidjaja

(LIPI). From the local news (www.detik.com), people are still worrying about the possible a big tsunamis after

the earthquake.

Earthquake

Date: Nov 17, 01:02:31 (Local time)

Location: Sulawesi subduction zone

Magnitude: Mw 7.6 (PTWC-R)

The following Fault Parameters, obtained from USGS CMT Solution, are adopted in the numerical simulation.

Focal Depth (meter) : 21000.000

Length of source area (meter): 70000.000

Width of source area (meter): 35000.000

Dislocation of fault plate (meter): 3.000

Strike direction (theta) (degree): 275.000

Dip angle (delta) (degree): 63.000

Slip angle (lamda) (degree): 90.000

Location of epicenter (Latitude, degree): 1.215

Location of epicenter (Longitude, degree): 122.200Note: width and length are estimated via empirical relationship by Wells and Coppersmith (1998).

Seafloor deformation

The seafloor deformation is calculated based on the elastic fault plane theory by Okada (1985). And the sea

surface elevation is assumed to exactly mimic the seafloor displacement (Figure 1).

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Figure 1 Seafloor deformation (Okada, 1985) Figure 2 Max amplitude distribution within 2 hours

Numerical Simulation

Linear shallow water equations in Spherical Coordinate (COMCOT) are implemented in the simulation with a

grid size 2 minutes and time step 3.0 seconds. Vertical wall boundaries are set up at 10.0-meter depth contour.

Tsunami amplitude distribution and snapshots of wave field are given in Figure 2 and 3.

Figure 3 Snapshot of tsunami wave field at 30 and 60 minutes after the earthquake