Test: Earthquakes - Class 9 MCQ

Earthquakes are most commonly found along plate boundaries, where tectonic plates interact. This region is where most seismic activity occurs due to the stresses and strains from plate movements, making it a hotspot for earthquake occurrence worldwide.

The Richter scale quantifies earthquakes by measuring the amplitude of seismic waves recorded on a seismogram. This scale provides a numerical value that indicates the energy released during an earthquake, allowing for a standardized comparison of earthquake magnitudes.

The Mercalli Scale measures earthquake intensity based on observed effects on people, buildings, and the Earth's surface. Unlike the Richter Scale, which quantifies energy release, the Mercalli Scale provides a subjective assessment of an earthquake's impact, helping to gauge its real-world consequences.

The intensity of seismic waves decreases steadily as they move away from the epicenter. This is because the energy of the waves disperses over a larger area, resulting in weaker vibrations felt at greater distances from the source of the earthquake.

A seismograph is the device used to measure and record the details of an earthquake, including its force, duration, and direction. The data collected helps scientists analyze the characteristics of seismic events and assess their potential impact on affected areas.

Tsunamis can be triggered by underwater earthquakes. When an earthquake occurs beneath the ocean, it can displace a large volume of water, generating powerful waves that travel across ocean basins, leading to devastating impacts on coastal communities.

Most earthquakes are primarily caused by the movement of tectonic plates, which are large sections of the Earth's crust. When these plates slide past or collide with each other, they create faults that can trigger seismic activity. This natural process is a fundamental aspect of the Earth's geological dynamics.

The focus of an earthquake is the point inside the Earth's crust where the movement begins. It is crucial to understanding the earthquake's dynamics, as it determines the depth at which the seismic waves originate, influencing the extent of the shaking felt at the surface.

Isostatic disturbances can cause earthquakes by disrupting the balance between land and sea, such as when sediments are deposited on ocean floors. This alteration in weight distribution can lead to movements in the Earth's crust, triggering seismic activity in the process.

One constructive effect of earthquakes is the creation of new landforms, such as lakes and altered coastlines. These changes can improve navigation and biodiversity in affected areas. While earthquakes are often destructive, they also play a role in reshaping the Earth’s landscape positively.