The door knockers of Mansurah: Strong shaking in a region of low perceived seismic risk, Sindh, Pakistan

Mansurah, the eighth-century Arabic capital of Sindh province, Pakistan, flourished for a mere 200 yr. Its destruction by an earthquake ca. 980 A.D. was first proposed by archaeologists who reported the discovery of crushed skeletons amid dateable coins found among its rubble. An abrupt natural death to the city was challenged by others who noted that the absence of wood or valuables was consistent with the city being sacked and systematically looted. The recent discovery of four decorated door knockers beneath the collapsed walls of one of the largest structures in Mansurah, however, reopens the case for an earthquake, since an invading army would almost certainly have removed them as booty. We suggest that an earthquake not only destroyed the city and its suburbs (intensity ≈ VIII), but resulted in postseismic avulsion of the river on which its citizens depended for agriculture, sanitation, and trade. Since natural levees have been observed in India to collapse in intensity VII shaking, it is unnecessary to invoke coseismic uplift as a requirement for upstream river avulsion. The absence in the past two centuries of large earthquakes in the region has resulted in central Sindh being depicted as a region of low seismic hazard, yet in 1668, in the same province, an earthquake destroyed nearby Samawani and also initiated avulsion of the Indus. A case can be made for reevaluating the five millennia of archaeological ruins in Pakistan to establish a long-term view of seismicity unavailable from the short instrumental record. Bilham, R. , and Lodi, S. , 2010, The door knockers of Mansurah: Strong shaking in a region of low perceived seismic risk, Sindh, Pakistan, in Sintubin, M. , Stewart, I.S. , Niemi, T.M. , and Altunel, E. , eds., Ancient Earthquakes: Geological Society of America Special Paper 471, p. 29–37, doi: 10.1130/2010.2471(03). For permission to copy, contact editing@geosociety.org. © 2010 The Geological Society of America. All rights reserved. 30 Bilham and Lodi spe571-03 page 30 Bhamanabad (Farooq, 1986). The evolving discussion concerning the nomenclature of the site and nearby urban centers can be followed in Elliot (1867), Cunningham (1871), Haig (1874, 1894), Raverty (1893), Cousens (1905, 1929), Panhwar (1983a, 1983b), Wheeler (1992), Hodīvālā (1939), Farooq (1986), and most recently Khan (1990). To avoid confusion, and since the identification of the city with earlier ones is irrelevant to the present discussion, we shall refer to the ruins as Mansurah. The vast area of rubble (2 km × 1.5 km) and the apparently orderly layout of the city led Bellasis to characterize Mansurah as the “Pompeii of the East,” a city frozen in time with many of its citizens interred within its ruins. The ruins are located 30 km east of the present path of the Indus, 60 km NNE of Hyderabad and 16 km ESE of Shahdadpur, Pakistan (Fig. 1). They consist of heaps of fragmented bricks separated by rubble-clogged ancient streets in orthogonal rows on a gently undulating area elevated above the meander of an abandoned river (Figs. 2 and 3). Mansurah was a planned city. Some of the streets were 65 m wide and were paved with bricks usually laid on edge (longest and narrowest dimension down), and underlain with wastewater drains (Farooq, 1986). In places, wastewater and sewage were led via conduits to terracotta-lined soakaway pits (Khan, 1990). The ruins are encircled by the remains of a 3-m-wide fortified wall with a perimeter length of 6.4 km, which some accounts (Elliot, 1867) describe as being surmounted by 1200 bastions— clearly an exaggeration if these ornamented the perimeter of the main city. A more conservative estimate is provided by Abul Fazl writing in the sixteenth century (Jarrett, 1891), who enumerated the number of ruined bastions as 140, spaced ~50 m apart (Cunningham, 1871). This very closely matches the measured perimeter, which would have required a 45 m mean spacing between 140 bastions. Khan (1990) describes the bastions as semicircular and spaced at 33 m intervals with remnants found at a height of 3.5 m. The remains of the bastions are now indistinguishable from the irregular mounds that characterize the level of the city. The several Arabic accounts that describe the founding of the city describe it as an island surrounded by a branch of the Mihran (the Indus). It was noted for its verdure and cleanliness, although some accounts complain of abundant fleas (Elliot, 1867). In the nineteenth century, at the time of the annexation of Sindh to India, the region was arid, with water found only in wells. Twentieth-century irrigation fed by the nearby Jamaro canal has now ponded parts of the abandoned river, which is distinctly concave where it abuts the eastern walls of the city. Elsewhere the ancient path of the river is obscured by agriculture. The description of the city as occupying an island is consistent with its current elevation 5–10 m above the shore of the present water in the river. The straightness of the SW wall and its continuation to a contiguous ruined settlement to the SE are suggestive of the existence of an artificial moat to the SW rather than a river meander. The path of the Jamaro canal was excavated with a 5° inflection to avoid crossing the Mansurah ruins (Fig. 1). Dominating the ruins, there is a single masonry tower known as the Thul (Fig. 4) that afforded subsurface access to a well (Cousens, 1929). The bricks of the town consist of thin fired clay bricks cemented with mud, but in the Thul, these bricks were cemented above ground with a gypsum-based cement. The foundations of the Thul used much larger bricks. Few intact bricks remain in the town, presumably because they have been scavenged for construction elsewhere. Pottery shards and glazed Figure 1. Google map view of Mansurah and its suburbs. A canal passes SW and a drain runs NE of the ruins, which show as light gray. An oxbow lake has now occupied the formerly abandoned river to the east of the city. Arrows to the right show photo angles of Figures 2–4. Shahdadpur