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<br />[ have assumed a range of scarp heights to ca1c~.late an <br />estimate of the seismic moment for previous earthquakes in San <br />Luis Valley. The seismic moment (~ is given by <br /> <br />where µis the shear strength across the fault (assumed here to be <br />' 3X1011 dyne/cmZ, a typical value for crustal rocks), D is the <br />fault displacement during a single earthquake, L is the total <br />fault length (51 km from Kirkham and Rogers) and h is the depth of <br />dislocation from surface down dip (17 km, typical of Basin and <br />Range faulting). The L H terms constitute the area of an asperity <br />along the Sangre de Cristo fault which might be expected to rupture <br />in the future. <br />From the seismic moment, an estimate of earthquake <br />magnitude (M) can be obtained from <br />M = 2/3 Log M, - 10.7 (2) <br /> Table II presents results of calculations using equatians (1) <br /> and (2) for the Sangre de Cristo fault. These estimates are <br /> Lower than the magnitude (M = 7.7) estimated by Kirkham and <br /> Rogers, but where equations (1) and (2) have been comp.sred with <br /> magnitudes calculated using seismographs, they seem to under- <br /> predict the magnitude by up to one half of a magnitude interval. <br /> Hence, the magnitudes on Table II may display the ranges <br />th <br />ti <br />l <br />l <br />h <br />i <br />di <br />d b <br /> va <br />ues. <br />e paren <br />e <br />ca <br />n <br />cate <br />y t <br /> Using the estimates in Tables I and II and Figure 1 a <br />' preliminary estimate of the earthquake probability can be made. <br /> 1da11ace (1970) has proposed the following equation to represent <br /> the average recurrence interval for an active Fault <br /> <br />5 <br />