Seismic and volcanic hazards affecting the vulnerability of the Sana’a area of Yemen

Abstract

Abstract The City of Sana’a is a World Heritage Site, renowned for its ancient tall and ornate domestic dwellings. Following a moderate, but locally destructive seismic event near Sana’a (Dhamar) in 1982 ( M s 5.5–6.0), the seismic vulnerability of the city and its hinterland have been reviewed, using the extensive records of the Arab chroniclers, going back over 1500 years. A hazard study indicated that Yemen is a country of moderate seismicity rather than one of low seismicity as previously considered, as records indicated that moderate-sized earthquakes ( M s 4.0–6.0), have occurred regularly over the last 1000–1500 years. It was determined that Sana’a is in a location where a damaging event could statistically occur every 200 years or so. Using a seismic character similar to that of the 1982 Dhamar event (shallow hypocentre, 40 s duration, peak ground acceleration 0.3 g , and M s 5.5–6.0), the vulnerability of Sana’a was determined from condition surveys of some 250f the historical houses, which proved remarkable levels of active structural distress and fabric decay. It was estimated that nearly 680f the building stock in Sana’a would be severely damaged to totally damaged beyond repair by a similar earthquake, causing a significant loss of life and destruction of a World Heritage Site. Strategies and techniques for reducing the vulnerability of the urban fabric of Sana’a, ranging from simple upgrading within the owners’ means to significant engineering measures, sympathetic to the historical and archaeological fabric of the buildings, are considered. Also considered are volcanic hazards, as records indicate that closely related to the seismic activity in Yemen are occasional, generally small-scale, volcanic eruptions. Several eruptions are indicated to have occurred in the Sana’a area over the last 1500 years, and the area is vulnerable to future eruptions. An event in about AD 200 is indicated by archaeological work to have overwhelmed several religious sites 20 km north of Sana’a.