An IoT-Based Earthquake Warning System for Smart Cities

Introduction

Natural disasters are sudden events caused by environmental factors that threaten lives, property and the ecosystem. Every year, they kill and maim people and damage property. Earthquakes and floods strike anywhere on earth, often without warning. In India, earthquakes are commonly occurring natural disasters. They are among the most deadly natural hazards and frequently cause surface faulting, tremors, liquefaction, landslides, aftershocks and/or tsunamis. Nearly59% of India’s landmass is subject to moderate and severe earthquakes that strike without warning. Earthquakes in India are caused by the movement of the tectonic plates. A tectonic plate is a massive, irregularly shaped slab of solid rock (WHO – Technical Hazard Sheet, 2018)http://www.who.int/hac/techguidance/ems/earthquakes/en/.

The internal structure of the Earth has three major layers:

• •

  Crust

• •

  Mantle

• •

  Core

The outer layer of the Earth is called the crust/lithosphere, which is very thin when compared to the other layers, and is broken into several large pieces called plates. The mantle consists of the upper mantle and the lower mantle. The plates of the Earth move because of the movement of the mantle. The center of the Earth is its core, which is nearly twice as dense as the mantle. The pattern of earthquake occurrences reveals that earthquake activity has occurred in a number of different earthquake belts (Stein &Wysession, 2003).

Earthquakes are happenings experienced during sudden movements of the Earth's crust. The upper part of the mantle, called the asthenosphere, is composed of liquid rock and lies under the Earth’s crust. The plates of the Earth's crust which “float” on top of the asthenosphere layer are forced to shift as the outpouring molten material below moves. A huge amount of energy is released in the form of waves as these plates shift and interacts with each other. Though earthquakes can take place anywhere on the planet with little or no warning, a large number of severe earthquakes occur near plate boundaries, as the plates converge (collide), diverge (move away from another), or shear (grind past one another).Earthquakes can also be triggered by means of moving rock and magma within volcanoes. During the collision, divergence and shearing of plates, large sections of the crust can fracture and move back and forth to disperse the energy released. This “shaking” is felt as a sensation during an earthquake (Mooney, 2002).

Figure 1.

Major Seismic Belts of the Earth

(Source: Geology Universe)

Figure 1 shows the earthquake belt, which is a narrow zone on the earth’s surface around which a majority of earthquakes take place.

Figure 2 shows the nine major plates: North American, Pacific, Eurasian, African, Indo-Australian, Australian, Indian, South American, and Antarctic. The Pacific Plate is the largest at 39,768,522 square miles. The Whole of India lies on the Indian Plate, whose relative motion is at a velocity of 5cms per year in the north-northeast direction (Srivastava, 2015).

At the subduction zones, two tectonic plates meet and one slides beneath the other, curving into the mantle (the layer underneath the crust). The plates move in different directions and strike against their neighbors at boundaries. The huge forces thus generated at plate boundaries cause volcanic eruptions and earthquakes. An earthquake is a vibration of the Earth’s surface caused by waves coming from a source of disturbance inside the earth (Oskin, 2015).