Seismic Risk, Vulnerability and Casualty Assessment in the Chahno District of Mashhad

Abstract & Introduction

As part of my studies in Disaster and Risk Management, I conducted a coursework report and research project aimed at assessing the potential casualties and damages resulting from earthquake hazards in the Chahno district of Mashhad, Iran.

In this report, a seismic scenario was considered for the city of Neyshabur, located approximately 75 kilometres from Mashhad. From a crisis-management perspective, I evaluated the structural and infrastructural characteristics of the area, including non-structural elements, road networks and vital arteries. Field-visit images were also documented.

The results indicated that in the event of a Mercalli Intensity VII (magnitude 5.5 to 5.9) earthquake with a maximum acceleration of 130 gals, approximately 25 nighttime casualties are projected if emergency-response teams are unavailable. These findings underscore the precarious situation of the region; moreover, due to its aging infrastructure, the area requires reconstruction and urban renewal.

Location of the Chahno district

The location of the Chahno district of Mashhad and its surroundings within the study area.

Historical earthquakes

Some of the historical earthquakes that have affected the city of Mashhad are shown in the table below, with their moment magnitude (Mw), epicentral distance and causative fault identified.

Damage estimation

Based on the field study and considering the structure types and their damage functions per the Japanese agency (JICA) studies, and assuming a magnitude 7.4 earthquake scenario in Neyshabur at 74 kilometres from Mashhad, a Mercalli intensity of VII was determined for the study area. As a result, the number of damaged building units was estimated at about 42.7 units and the overall damage ratio at 12.87 percent.

Damage broken down by structure type.

Human casualty estimation

Estimating casualties from building collapse requires two kinds of information: the number of occupants of collapsed buildings, and the ratio of casualties to those occupants. This study adopts the fundamental casualty-estimation method proposed by Coburn et al. (1992), since it derives from statistical considerations of earthquake losses worldwide, including Iran.

Estimation formula: Ks = D5 * M1 * M2 * M3 * (M4d + (1 - M4d) * M5)

Ks: human casualties — D5: number of collapsed buildings — M1: occupants per building — M2: building occupancy state at the time of the earthquake — M3: occupants trapped in collapsed buildings — M4d: casualty ratio immediately after collapse — M5: ratio of the injured who die before rescue.

Assuming a Mercalli intensity of VII and a peak acceleration of 130 gals, the number of casualties was estimated. Here, casualties are only those killed as a result of building collapse. Due to insufficient information on the seismic zonation of Mashhad, casualties were computed based on the Neyshabur earthquake alone.

Conclusions & recommendations

The study area does not have sufficient strength and capacity to face an earthquake crisis; therefore, to reduce losses and save lives, action should be taken as soon as possible:

1) A comprehensive earthquake crisis-management and prevention plan prepared by the district municipality.

2) Taking the role of the public seriously as a fundamental pillar of crisis management, from education to implementation and oversight.

3) Strengthening critical structures (schools, clinics, police centres) and building more fire stations and medical centres.

4) Allocating evacuation and shelter sites; a clear shortage of open space was evident in the study area.