Reconnaissance report on the 12 October 1992 Dahshur, Egypt, earthquake

Abstract

The 12 October 1992 earthquake (MB 5.9; Ms 5.2) that occurred near the village of Dahshur, Egypt, was the latest in a long history of earthquakes that occasionally cause damage to buildings in Cairo and surrounding areas in northeastern Egypt.The epicenter of the earthquake was about 18 km south of the center of Cairo and located at a depth of about 25 km.Damage to engineered buildings in Cairo appeared to be mainly due to poor construction materials, poor construction detailing, overloading of building columns beyond their design values, inferior workmanship, or deficient foundation systems.Damage to non-engineered structures, such as dwellings, was substantial in the earthquake region, particularly for adobe construction.Adobe is known to be one of the most vulnerable building materials to earthquake shaking; widespread use of this material in villages along the Nile valley contributed significantly to the high number of deaths and injuries from this moderate-sized earthquake.Inspections of bridges across the Nile and overpasses in Cairo revealed no earthquake damage.Geologic effects of the earthquake were minimal, restricted to a small area of minor liquefaction near the village of Manshyat Fadil on the west side of the Nile, approximately 20 km south of the epicenter.The area of liquefaction coincided with the severest shaking damage from the earthquake in Manshyat Fadil.Field investigations by motor vehicles and by airplane revealed no surface fault rupture from the earthquake.That more widespread damage did not occur in the Cairo metropolitan area was due to the moderate size of this earthquake.However, considerable vulnerability to earthquake shaking exists in the Cairo building stock and far more severe effects would be expected from a somewhat larger earthquake in the vicinity of Cairo, or from an earthquake of comparable magnitude directly under the city.The important lesson learned from this earthquake was not of a technical or scientific nature.Rather, it was the tragic demonstration of the potential for catastrophe in metropolitan Cairo if the warning of this moderate earthquake is not heeded in future development, planning, and earthquake preparedness.With this lesson in mind, we offer the subsequent recommendations on an earthquake preparedness strategy for the region affected by the 12 October 1992 Dahshur, Egypt, earthquake.They are divided into three categories: A) Engineering design and building code development, B) Scientific and engineering research needs, and C) Civil preparedness and governmental disaster response. A. Engineering Design and Building-Code Development:An earthquake itself does not pose a significant threat to people.Rather, it is the damage to, and collapse of buildings and other structures that result in casualties and fatalities.If construction practices are improved so that buildings withstand the expected earthquake ground motions with less damage and without collapse, lives will be saved and the number of injuries will be reduced.Much engineering knowledge has been gained from the study of earthquake effects on all types of construction around the world and the task of improving building construction and design begins with communicating this knowledge to local authorities and the local engineering community.Significant improvement to the earthquake resistance of common structures, such as dwellings, can be made with little additional cost if proper construction techniques are used.A lasting contribution to improved earthquake-resistant design for all types of construction is to formalize appropriate earthquake-resistant construction techniques into a building code.Equitable application of building-code requirements throughout a region follows a scheme of zoning based on the prevalent earthquake ground-motion hazard.Thus, the ground-motion hazard needs to be quantified in hazard maps for rational decisions to be made on the degree of earthquake resistance that is required of construction in any particular area.Seismic-hazard maps of this type have also found wide-spread use in land-use planning and insurance analyses.Recommendations in this category are aimed at near-term objectives (approximately three years or less to realize results) to deal with the immediate earthquake information needs of the practicing engineers and government agencies charged with overseeing construction practice.The recommendations, in large part, implement common knowledge that has been gained from earthquake experiences around the world.1. Establish an influential task force consisting of knowledgeable engineers, seismologists, and geologists from various sectors ~ academic, private, government ~ to motivate professional and governmental concern and understanding of earthquake mitigation measures.Such a body could form the core group of a local professional organization promoting earthquake education and governmental earthquake-mitigation policy.2. Quantify the earthquake ground-motion hazard throughout Egypt, with particular attention to northeastern Egypt and the vicinity of Cairo, in terms useful to modern engineering design and code development, land-use and economic planning.3. Qualitatively establish the vulnerability of various types of common, high-occupancy construction in Cairo to earthquake shaking for estimates of earthquake risk (monetary loss) from past or potential earthquakes.4. Establish earthquake-engineering-related curricula in the university system and encourage faculty and engineering students to become involved in all aspects of earthquake mitigation engineering including earthquake reconnaissance, recovery and reconstruction.5 Conduct fora for exchanging information.Most observed damage to engineered buildings in the Dahshur earthquake was due to poor detailing and/or quality control.Commonly known errors made during design and construction of earthquake resistant structures could be avoided with simple communication/education vehicles, such as workshops and professional meetings, in which experts are brought together with practicing engineers and local authorities to exchange information on "lessons learned" from past earthquakes.6. Provide guidance and education for non-engineered construction to the general public through information campaigns (see C below).7. The General Authority for Roads and Bridges should adopt established standards for the retrofit of bridges and overpasses.