Evidence for Tectonic Activity During the Mature Harappan Civilization, 2600-1800 BCE

The mature Harappan civilization located in Pakistan and India dates from 2600 to 1800 BCE. By combining seismic data, three-dimensional elastic dislocation modeling, and archaeological findings we examined the role that earthquakes played in the demise of Harappan settlements. The study focuses on three different geographical regions: Gujarat, the Sarasvati-Ghaggar-Hakra River valley, and the Makran coast of Pakistan. In Gujarat, the fluvial system of the Rann of Kachchh has undergone significant changes. The Rann of Kachchh formed as a delta for three rivers, becoming an inland sea during the time of Alexander the Great, and ultimately a salty marsh. These changes were brought about by a combination of sea level changes, the truncation of the three rivers by tectonic uplift and the deepening of the Rann by earthquake induced subsidence. Events analogous to the 1819 Allah Bund earthquake, which dammed the Puran River for seven years, would have significantly altered the water source for downstream settlements. Data from the recent 2001 Bhuj event shows that Harappan settlements would have suffered considerable shaking damage from an analogous historical event. Archaeological studies to date have found direct evidence for of at least one large earthquake at Dholavira in 2200 BCE. A number of the mature Harappan settlements are located along the dry Sarasvati-Ghaggar-Hakra river system. The decline of these sites coincides with the divergence of the Sarasvati-Ghaggar-Hakra system to the Indus and Ganga river systems. A succession of earthquakes, along with a period of aridity, likely led to the disappearance of the Sarasvati-Ghaggar-Hakra system. Although this region has not had any large earthquakes in historic times, there is archaeological evidence of two large events at the Harappan site of Kalibangan, at 2900 and 2700 BCE. Along the Makran coast two settlements, believed to have been Harappan seaports, are now located tens of kilometers inland. Changes in sea level, along with tectonic uplift from great Makran subduction zone earthquakes, can explain the conundrum of why these sites are now tens of kilometers inland. Dislocation modeling demonstrates that several great subduction earthquakes in the historical past could easily have raised the Harappan settlements to their current inland positions above sea level. The examples presented demonstrate that earthquakes affected the demise of several Harappan sites either by direct shaking damage, altering the water supply, or by changing the relative sea level.