Earthquakes and Seismic Activity

Questions and Answers

What are seismic zones and how do they differ from aseismic zones?

Seismic zones are areas prone to earthquakes, while aseismic zones are not prone to such events.

Describe the movement and characteristics of Primary waves during an earthquake.

Primary waves cause rock particles to vibrate in a push and pull manner and travel fastest through gases, liquids, and solids.

What is the difference between the seismic focus and the epicenter of an earthquake?

The seismic focus is the point within the Earth where the earthquake originates, while the epicenter is the point on the Earth's surface directly above the focus.

List two natural causes and two human causes of earthquakes.

Natural causes include tectonic movements and vulcanicity; human causes include underground nuclear explosions and mining explosions. Signup and view all the answers

Explain the role of tectonic movements in causing earthquakes.

Tectonic movements involve the shifting of tectonic plates, leading to energy release that manifests as earthquakes. Signup and view all the answers

What instrument is used to measure earthquakes and how does it function?

The seismograph measures earthquakes by using a pendulum to record seismic impulses on a seismogram. Signup and view all the answers

Describe the difference between intensity and magnitude in the context of earthquakes.

Intensity measures the strength of shaking experienced at a location, while magnitude quantifies the amount of energy released by an earthquake. Signup and view all the answers

What are the potential effects of an earthquake on infrastructure and human life?

Earthquakes can cause loss of life and property through building collapses, disrupt transport and communication lines, and trigger landslides. Signup and view all the answers

Where do earthquakes commonly occur in relation to tectonic plates?

Earthquakes commonly occur along the boundaries of tectonic plates, major fault zones, and areas of volcanic activity. Signup and view all the answers

What is a tsunami and how is it related to earthquakes?

A tsunami is a series of enormous sea waves caused by underwater earthquakes that can flood coastal areas. Signup and view all the answers

Study Notes

Measurement of Earthquakes

Seismograph is a pendulum-based instrument that records seismic impulses on a seismogram.
Earthquakes are measured by intensity and magnitude.

Intensity

Intensity refers to the strength of the quake's shaking, assessed through its effects on people, buildings, and structures.
Measured using the Mercalli Scale, which ranges from I-XIII:
- I: imperceptible shaking.
- V: strong enough to awaken sleepers; objects swing.
- VIII: destructive; gaping cracks in walls; some buildings collapse.
- XII: major catastrophe where every building is destroyed.

Magnitude

Magnitude measures the energy released by an earthquake on the Richter Scale, ranging from 0 to 8.9.
Intensity varies based on proximity to the epicenter:
- Intensity I correlates with magnitude 2.
- Intensity VIII correlates with magnitude 6.
- Intensity XII correlates with magnitude 8.5.

World Distribution of Earthquakes

Earthquakes are primarily located:
- Within zones of major faulting (e.g., the Rift Valley).
- In volcanic areas (e.g., Oldonyo Lengai in Tanzania).
- Along tectonic plate boundaries (e.g., Japan, the Philippines, and the coasts of North and South America).

Effects of Earthquakes

Can result in loss of life and property from building collapses.
Disrupt transportation and communication, severing pipelines and electricity lines.
Cause landslides that threaten lives and infrastructure.
Lead to changes in the sea floor and coastal regions.
Generate tsunamis, resulting in flooding of coastal areas.

Earthquake Characteristics

Earthquakes are sudden movements of the Earth's crust, occurring in seismic zones.
Three types of earthquake waves:
- Primary waves: fastest, cause push-pull vibrations, travel through gases, liquids, and solids.
- Secondary waves: cause vibrations at right angles to wave movement, can only move through solids.
- Surface waves: cause shaking at the surface, can lead to structural damage.
  - Rayleigh waves: cause elliptical movement of surface rocks.
  - Love waves: cause horizontal movement of rock particles at right angles to wave direction.
The seismic focus is the earthquake's origin point, with the vertical point above known as the epicenter.

Causes of Earthquakes

Natural Causes

Tectonic movements from shifting plates create tectonic earthquakes.
Vulcanicity caused by magma movement leads to sudden rock displacements.
Gravitational collapse of crustal rocks can trigger quakes.
Energy release in the mantle due to radioactivity produces shock waves.
Isostatic adjustments occur when continental masses rise to regain balance.

Human Causes

Underground nuclear explosions generate shock waves felt in nearby areas.
Train movements can induce ground vibrations.
Explosive use in mining and quarrying also results in measurable vibrations.

Description

This quiz covers key concepts related to seismic zones and the fundamental characteristics of earthquakes. It explores the differences between seismic and aseismic zones, the nature of Primary waves, and the roles of tectonic movements. Additionally, it discusses measurement instruments and the various causes of earthquakes.