Pakistan Earthquake of M7.7 Strikes September 24, 2013

A major earthquake of preliminary magnitude M7.4, later upgraded to M7.7, struck in south central Pakistan on Tuesday 24 September at around 4pm local time.

Early reports from the United States Geological Survey indicate that the tremor occurred at a depth of just 12.4 km: its epicenter was 41km from the town of Awaran.

Although at the time of writing there were reports of damage and limited casualties, the magnitude and depth of the earthquake are significant and potentially damaging.

USGS forecasts suggest a high probability of significant deaths as a result of the earthquake, although the fact that the region is relatively sparsely populated may turn out to have saved many lives.

The initial death toll, however, is likely to grow.

Pakistan’s M7.7 Quake: Tectonic Setting

Like many places in central Asia, Pakistan is highly vulnerable to earthquake activity. Tectonically speaking, the country is affected by two major continental collision zones – that between the Indian subcontinent and Eurasia (responsible for the uplift of the Himalayas) and that between the Arabian and Eurasian plates. The earthquake’s epicentre lies in a region influenced by both of these collisions so that without further detail on the mechanics of the tremor, it’s impossible to say for certain what was the cause.

Broadly speaking, the India-Eurasia collision is marked by a roughly north-south trending series of lateral (strike-slip) faults while the convergence of the Arabian plate with Eurasia is marked by a subduction zone, the Makran subduction zone, off the country’s southern coast.

The relatively close proximity of these (in geological terms) has given rise to a complex sequence of folded and faulted mountain ranges parallel to the coast and curving northwards to the west of the India-Eurasia convergence zone.

Pakistan’s Earthquake History

With so many forces at play, it’s unsurprising that Pakistan is subject to regular earthquakes, some of which can reach significant magnitudes. The largest event on record, an M8.0 in 1945, took place offshore and caused extensive damage and a tsunami: It killed an estimated 4,000 people.

Earthquakes of slightly smaller magnitudes have, however, proved much more deadly even in the recent past: a tremor of M7.5 in 1930 killed around 30,000 but even that was eclipsed by the 2005 event (M7.6) in which an estimated 80,000 people lost their lives as a result of the ‘quake and its aftermath.

Middle Eastern Earthquakes

More recently, the region has experienced significant tremors in recent months: April 2013 saw an M7.8 in Iran which, though in a separate state, resulted from the same regional tectonic influences and which caused extensive damage and several deaths across the region. Typically, though, Pakistan’s most devastating earthquakes are more likely to occur closer to the Himalayas, where compression is strong and complex, population density is high and there is a strong risk of secondary damage (for example from landslides and avalanches). Furthermore, these areas are not easily accessible, especially in winter, so that the initial problems are complicated by the challenges of providing earthquake relief.

Sources

Sky News online. Earthquake Measuring 7.8 Hits Rural Pakistan. (2013). Accessed September 24, 2013.

USGS. Historic world earthquakes. (2013). Accessed September 24, 2013.

USGS. M7.7 – 66km NNE of Awaran, Pakistan. (2013). Accessed September 24, 2013.

Yeats, R. Active Faults of the World. (2012). Cambridge University Press.