Date of Award


Document Type


Degree Name

Master of Science in Earth and Environmental Sciences


Geological Sciences

First Reader/Committee Chair

McGill, Sally


We studied a paleoseismic trench that was excavated across the Banning strand of the San Andreas Fault by Petra Geosciences (33.9172°, -116.538°). The trench exposed a ~40 m wide fault zone in interbedded alluvial sand gravel, silt and clay deposits. We present the first paleoseismic record for the Banning strand of the southern San Andreas Fault. The most recent event occurred sometime between 730 and 950 cal BP, potentially coincident with rupture of the San Gorgonio Pass thrust. We interpret that five earthquakes have occurred since 3.3-2.5 ka and eight earthquakes have likely occurred since 7.1-5.7 ka. It is possible that additional events may have occurred without being recognized, especially in the deeper section the stratigraphy, which was not fully exposed across the fault zone. We calculate an average recurrence interval of 380 - 640 yrs based on four complete earthquake cycles between earthquakes 1 and 5. The average recurrence interval is thus equivalent to or less than the elapsed time since the most recent event on the Banning strand. The recurrence interval is similar to the San Gorgonio Pass (450-1850 years) but longer than that for the Mission Creek strand (~220 years).

Additional Files

Plate1_FinalMosaics.pdf (53169 kB)