Modeling

Stress models were evaluated using Coulomb 1.0 modeling software (Toda et al., 1998)

Is observed faulting pattern consistent with regional strain field?

Basin and Range strain for the region was modeled using estimates determined by Marshall et al. 1997 and compared to Langbein et al. 1993 estimations. Using the background stress we compute the optimal orientation for strike-slip fault planes. Numerous values of the coefficient of friction were tested and higher values tended to give better results for NNE trending fault planes.


Coeffient of friction 0.4 and Marshall et al. 1997 Basin and Range strain rate	Coeffient of friction 0.8 and Langbein et al. 1993 Basin and Range strain rate.

Did the 1997 caldera deformation encourage 1998 and 1999 Hilton Block events?
	A case study for strain in the region was evaluated using the 1997 inflationary period and subsequent propagation of seismicity into the Hilton Block from early 1998 to Nov. 1999. A best fitting model of the 1997 inflationary period, which included two triaxial dikes inflating at depths of 6km and 15km (Langbein 1999, personal communication) was added to the Marshall et al. estimation of regional strain, as well as, estimations of right lateral motion in the south moat fault. The June 9th, 1998 and July 15th 1998 M5.1 events were modeled using the moment tensor solutions and aftershock distributions. Coulomb stress was tested at each interval to determine if the subsequent events increased stresses on the 1999 fault
Background strain and 1997 sources on June 9th, 1998 M5.1 right-lateral fault plane.	Background strain, 1997 sources on July 15th, 1998 M5.1 normal fault plane.
Background strain, 1997 sources and June 9th, 1998 motion on July 15th normal fault plane.	Background strain, 1997 sources and June 9th, 1998 motion on July 15th normal fault plane.
Background strain, 1997 sources and June 9th, 1998 motion on May 1999 left-lateral fault plane.	Background strain, 1997 inflationary sources, June 9th, 1998 motion and July 15th, 1998 motion on May 1999 left-lateral fault plane.