The maximum background earthquake (MBE) is the largest earthquake not associated with significant primary surface rupture. The MBE is estimated for the Basin and Range province considering 22 earthquakes from the province and a simple physical model of a circular rupture in the seismogenic zone. In the Basin and Range province, the number of historical earthquakes in the magnitude range 6 to 6.6 without significant surface rupture is clearly greater than the two events below magnitude 6.6 with primary surface rupture. Based on the historical record, the MBE for the Basin and Range province is magnitude 6.6, but given the various uncertainties involved, the usage of a magnitude value of 6.5 may be more reasonable for seismic hazard studied.

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