Seismology and Earthquake Origin Questions and Answers

Answer: C

It occurred far from any plate boundary in peninsular India, in an area previously thought quiet, and caused heavy loss of life because the shallow focus met unreinforced masonry housing. It showed that stable regions are not free of hazard.

Answer: D

Correct answer: reservoir-induced seismicity

The magnitude 6.3 earthquake near the Koyna reservoir in 1967 is the largest event anywhere attributed to reservoir impoundment, and seismicity has continued there for decades. The mechanism is that the water load and, more importantly, the increased pore pressure at depth reduce the effective stress on faults already close to failure, so they slip sooner than they otherwise would.

Answer: A

A shallow submarine thrust earthquake lifts or drops a large area of sea bed and displaces the whole water column above it. Strike-slip movement shifts the floor sideways and displaces far less water, which is why not every large submarine earthquake produces one.

Answer: B

Rupture of the plate boundary west of Sumatra lifted the sea floor over an enormous length and sent waves across the whole ocean basin. It prompted the establishment of warning systems in the region, including for the Indian coastline.

Answer: C

It covers both the sources of earthquakes and the waves they send through the earth, and the second has made it the main tool for studying the planet's interior. Structural response to that shaking belongs to earthquake engineering.

Answer: D

Correct answer: designing structures to withstand earthquake shaking

Earthquake engineering takes the shaking as given - supplied by seismology and hazard assessment - and asks how to build so that structures survive it with acceptable damage. Predicting earthquakes and characterising the crust are seismology’s problems; the engineer’s is the response of the structure.

Answer: A

Correct answer: frequency and distribution of its earthquakes

Seismicity describes the earthquake activity of a region: how many events, of what size, where, and how often. It is an observational characterisation drawn from instrumental and historical records, and it is the raw material from which recurrence relations and hazard maps are built. Rock strength and soil thickness are separate properties.

Answer: B

Correct answer: felt by people

Millions of earthquakes occur each year and the overwhelming majority are too small for anyone to notice, though modern networks record them routinely and assign them magnitudes. This follows directly from the Gutenberg-Richter relation: with a \( b \) value near one, each drop of a magnitude unit brings ten times as many events.

Answer: C

Correct answer: liquefaction, landslides, fire and tsunami

Shaking causes most of the damage but it also triggers a series of secondary hazards, and in some events these dominate the losses. Saturated loose sand can liquefy and lose bearing capacity; slopes fail; ruptured gas mains and fallen power lines start fires that spread through a city with a broken water supply; and offshore, sea bed displacement generates a tsunami.

Answer: D

Correct answer: a great earthquake

The conventional descriptive bands run from micro, minor and light through moderate and strong to major, with great reserved for magnitude 8 and above. Such events involve rupture over hundreds of kilometres of fault, occur roughly once a year worldwide, and are essentially confined to subduction zones and the largest continental thrust and strike-slip systems.