• Hundreds of tremors have hit the Greek island of Santorini in the past week, leading more than a thousand people to flee the tourist hotspot. 

• Known for its spectacular cliffside views and a dormant volcano, Santorini and neighbouring Aegean Sea islands have been hit by hundreds of tremors since last week, the largest with a magnitude of 4.9.

• The neighbouring islands of Anafi, Ios and Amorgos have also been affected.

• Santorini is among Greece’s premier travel destinations, with 3.4 million visitors in 2023.

• Santorini is part of the Cyclades group of islands. The Cyclades are a Greek island group in the Aegean Sea, comprising about 220 islands.

• The island, located on a volcanic hotspot in the Aegean Sea, has experienced frequent seismic activity, and while such tremors are common, the intensity and frequency in recent days have raised concerns. 

• Greece sits on multiple fault lines and is often rattled by earthquakes. One of the largest volcanic eruptions in history, around 1600 BC, formed Santorini in its current shape. 

• In 1956, a quake with a magnitude of over 7.0 left over 50 dead on Santorini and gutted hundreds of buildings.

Some terms related to earthquake

Earthquake: An earthquake is a sudden, rapid shaking of the ground caused by the shifting of rocks deep underneath the earth’s surface. Earthquakes can cause fires, tsunamis, landslides or avalanches. Earthquakes are classified as, Slight (M<5.0), Moderate (5.0<M<6.9) and Great (M>7.0) depending upon the magnitude on the Richter scale. An earthquake having a magnitude, M<2.0 is termed as a microearthquake. 

Seismograph: A seismograph, or seismometer, is an instrument used to detect and record earthquakes. Generally, it consists of a mass attached to a fixed base. During an earthquake, the base moves and the mass does not. The motion of the base with respect to the mass is commonly transformed into an electrical voltage. The electrical voltage is recorded on paper, magnetic tape, or another recording medium. This record is proportional to the motion of the seismometer mass relative to the earth, but it can be mathematically converted to a record of the absolute motion of the ground. Seismograph generally refers to the seismometer and its recording device as a single unit.

Richter scale: The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake. 

Epicenter: It is the point on the surface of the Earth, vertically above the place of origin (hypocenter or focus) of an earthquake.

Fault: A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake — or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.

Aftershock: An earthquake that follows a large magnitude earthquake called, “main shock” and originates in or around the rupture zone of the main shock. Generally, major earthquakes are followed by a number of aftershocks, which show a decreasing trend in magnitude and frequency with time.

(The author is a trainer for Civil Services aspirants.)