Civilizations have existed in the proximity of the Indus River Valley regions of modern Pakistan and India from at least 3000 B.C. onward. Geographically, the region encompasses a swath of the Makran coast, the alluvial plain and delta of the Indus River, and the Runn of Kachchh. The regional tectonic setting is controlled by the collision of the Indian and Eurasian plates and the subduction of the Arabian plate beneath the Eurasian plate. Earthquakes have undoubtedly struck many ancient sites, but finding their footprint in a riparian environment represents a challenge for archaeoseismology. However, some insight into seismoarchaeological indicators can be gleaned from examining the earthquake effects produced by historical infrequent large-magnitude events that have occurred in the region. Studies of these earthquakes emphasize the importance of repeated reconstructions, direct faulting, river damming from seismic uplift, and coastal elevation change as indicators of past earthquakes. Examples of past earthquake effects are presented for Banbhore in the Indus Delta, Brahmanabad, and the Harappan sites of Kalibangan and Dholavira. Future hermeneutic investigations in the region need to incorporate a seismological/tectonic perspective and not rely solely on serendipity.

Abstract More than 3,000 gravity observations in the Northern Gulf province, including an underwater gravity survey of the Salton Sea, show the over-all trend of isogal contours to be northwest, parallel to the tectonic pattern dominated by the San Andreas fault system. Contours northeast of the trough trend east, probably reflecting Transverse Range structures in this area. A prominent and linear gradient of 5 mgal/km marks the Banning-Mission Creek fault in the Coachella Valley but dies out southeastward at about the same point the surface trace disappears. The San Jacinto fault zone is characterized by a series of maxima and minima that tend to confirm continuity of this fault zone to the Gulf of California. A 15-20 mgal maximum over the Obsidian Buttes suggests a large anomalous mass at depth, or may be related to contemporaneous metamorphism of the Tertiary sedimentary section that has recently been observed in nearby steam wells. The regional gravity gradient indicates a crustal thickening northwest from the Gulf of California; inferred crustal thicknesses are 32 km at the International Border and 40 km at San Gorgonio Pass. Ten seismic refraction profiles in the Imperial and Coachella Valleys indicate several throughgoing velocity zones, but we are unable to correlate these with known stratigraphic units. The maximum thickness of sediments in the trough appears to be about 6.4 km (21,000 ft) just south of the International Border, with basement becoming shallower both to the north and south. The Salton trough has many geophysical and structural similarities to the Dead Sea rift, but the markedly en echelon pattern of major faults in the Salton trough and Gulf of California appears unique. A particular problem is presented by their orientation, which would suggest left-lateral displacement across the zone rather than the right-lateral displacement that is known to characterize at least the northern end of the province.