Kentucky Geological Survey Report of Investigations


Predicting strong ground motion from a large earthquake depends to a large extent on the development of a realistic source model. Strong ground motion was simulated using the composite source model. F0or comparison purposes, two different approaches were implemented in the source procedure simulation. For the first approach, the source was taken as a superposition of circular subevents with a constant stress drop. The number of subevents and their radii followed fractal law distribution, specified as a spatial random field, and subevents were allowed to overlap. This resulted in the total area of the subevents being much greater than the area of the main event, in order to catch the total seismic moment conservation. For the second approach, the number of subevents and their characteristic dimensions still obeyed fractal law, but subevents were distributed randomly over the main fault and did not overlap. The total area of subevents equaled the area of the main fault. In the second approach, the subevent stress drop was left as a free parameter to be adjusted, so that the sum of the subevents’ seismic moment equalled the seismic moment of the main event. Using these two approaches, broadband ground motion was predicted from scenario earthquakes. The numerical simulations from these two approaches gave us similar results in waveform, peak ground motions, and frequency contents.

The major purpose of these simulations was to address some recent criticism of the overlapping procedure (e.g., numerical implementation) used in the previous composite source model. The generally good agreement between simulated and observed ground motions from the Mw4.6 June 18, 2002, Darmstadt, Ind., earthquake and the Mw4.0 June 6, 2003, Bardwell, Ky., earthquake shown in this study indicates that the numerical techniques of the composite source model are capable of reproducing the main characteristics of ground motion, both in the near field and the far field, in the central United States.

Publication Date



Series XII

Report Number

Report of Investigations 14

Digital Object Identifier (DOI)

Included in

Geology Commons