Abstract In 1886, a large earthquake (∼M6.9–M7.3) rocked the Summerville-Charleston South Carolina area along the southeastern coast of North America. The largest east coast earthquake in North America, the earthquake caused massive damage to the cities and left ∼100 people dead. No surface rupture has ever been located; however, ongoing seismicity and damage from the 1886 earthquake has helped scientists to locate the active faults at depth and to identify potential surface offsets. The first day of the field trip will look at the damage from the earthquake as a means of understanding more about the mechanics of the earthquake. As the field trip moves into downtown Charleston, the damage will be examined as a proxy for how earthquakes cause buildings to fail and the type of damage a future earthquake could cause. The ongoing seismic activity along the suspected causal faults suggests that the earthquake risk in the Summerville-Charleston area remains high, and so the second day of the field trip will focus on the potential effects of a moderate to large earthquake in the region of the 1886 earthquake. One of the unique features of the Charleston-Summerville area is the high potential for widespread liquefaction and damage to the many bridges in the area. Therefore, Day 2 will focus on the potential for damage from a major earthquake on bridges and highly liquefiable sites by visiting a bridgeport area and then a barrier island. The visit to the barrier island highlights one of the main problems in Charleston in the event of an earthquake, the isolation of communities, with over 720 bridges and many more culverts in the area it is expected that people will be isolated in small communities for long periods of time.

We undertook a parametric study, using a two-dimensional distinct element method, to investigate if there is a preferred geometry of intersecting faults that may favor the occurrence of intraplate earthquakes. This model subjects two and three vertical, intersecting faults within a block to a horizontal force across them, representing the maximum horizontal compression (S Hmax ). The main fault is oriented at an angle α with respect to S Hmax , and β is the interior angle between the main fault and the intersecting fault. The third fault is oriented parallel to the main fault and is half its length. The distribution of shear stresses is examined along the faults for different values of α and β, and varying lengths of the main and intersecting faults. In all cases, maximum shear stresses are generated at the fault intersections. The modeling results reveal that the magnitudes of the shear stresses depend on the values of α and β, with an optimum range for α between 30° and 60°. In the case where the sign of the shear stress on the intersecting fault is opposite that on the main fault, the largest stresses at the fault intersections are obtained when β is between 65° and 125°. When the stresses on these two faults are of the same sign, the largest stress values at the intersections are obtained when 145° ≤ β ≤ 170°. The results of the modeling are consistent with the observed geometry of faults in the New Madrid and Middleton Place Summerville seismic zones.