The Earthquake Engineering Online Archive

Near-Fault Seismic Ground Motions

Dreger, Douglas S.; Hurtado, Gabriel; Chopra, Anil K.; Larsen, Shawn C.

UCB/EERC-2007/03, Earthquake Engineering Research Center, University of California, Berkeley, 2007-10-26, PDF (4.1 MB)

Bridges that cross faults are subject to static deformation that occurs at almost the same time as the arrival of dynamic pulse-like ground motions. Static offsets can be as large as several centimeters to many meters and strong ground motion velocity pulses exceeding 100 cm/s have been observed. Near-fault records, in the distance range of 10 to 100s of meters from faults are essentially nonexistent except for a few cases and therefore numerical simulation of ground motions for such near-fault situations is necessary. The paper presents simulated ground motions to 17.5 Hz, 15-100m from the fault for a Mw6.5 earthquake using an elastic finite-difference code. Simulations for homogeneous earth structure are compared for uniform and heterogeneous fault rupture scenarios. To investigate asymmetry of ground motions on opposite sides of a dipping reverse fault the dislocation method of Okada (1992) is used to compute static offset. From those results a simplified procedure for the simulation of near-fault time histories is developed. All of the simulations assume linear elasticity, and it is noted that the computed strain is as high as 10-4 - 10-3, and it is likely that there would be significant non-linear behavior in this near-fault region.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-07-03.pdf (3 MB)