The Ground Beneath Twenty Million People: What is known about Karachi's earthquake risk, and what is not
1 The faults around Karachi The outer shell of the earth is broken into large rigid pieces called tectonic plates. They move slowly and constantly in different directions. Where they meet, they grind against one another, and the stress that builds up along those contacts is released as earthquakes. Karachi lies roughly 150 kilometres east of a point where three of these plates meet: the Arabian plate, the Indian plate and the Eurasian plate. The Arabian plate is moving towards Eurasia at 28 to 33 millimetres a year, about the speed at which a fingernail grows. Over a century that is three metres of accumulated movement. Box 1.1 What is a fault? A fault is a fracture in the rock of the Earth's crust where two blocks of rock can slide past one another. Most faults are not visible at the surface. Many lie buried under sediment, roads and buildings. A fault is described as active if it has moved in the recent geological past and is expected...