Earthquakes, Faults, Mountain Belts & Plate Tectonics – Week 1–3 Lecture

47 question-and-answer flashcards covering definitions, processes, examples, and comparative facts on earthquakes, seismic waves, faults, mountain belts, volcanoes, plate tectonics, and lithosphere characteristics from the Week 1–3 Science 10 lecture.

What is an earthquake?

A sudden and violent shaking of the ground caused by movements within the Earth’s crust or by volcanic action.

Why do earthquakes occur?

They happen when underground rock suddenly breaks along a fault, releasing energy that travels as seismic waves.

How do rocks behave along a fault before an earthquake?

Blocks of rock stick and catch on each other instead of sliding smoothly, storing strain until they break.

What were the key details of the 27 July 2022 Abra, Philippines earthquake?

Magnitude 7.0 at 8:43 a.m.; epicenter in Tayum, Abra (17.64° N, 120.63° E) at 17 km depth; felt across Northern Luzon and Metro Manila.

Define epicenter.

The point on Earth’s surface directly above the earthquake focus.

Define focus (hypocenter).

The point within Earth where seismic energy is first released, directly below the epicenter.

What does earthquake magnitude measure?

The relative size or energy released by an earthquake; higher numbers mean stronger quakes.

What instrument records ground motion during an earthquake?

A seismograph or seismometer.

What is a seismogram?

The paper or digital record produced by a seismograph, showing ground motion over time.

What are seismic waves?

Energy waves released by an earthquake, recorded by seismographs and also called earthquake waves.

Differentiate body waves and surface waves.

Body waves travel through Earth’s interior; surface waves travel along Earth’s crust.

Which seismic wave travels fastest?

Primary (P) waves.

Describe P-wave particle motion.

Longitudinal; particle motion is parallel to the direction of wave propagation.

Through which materials can P-waves travel?

Both solids and fluids (liquids & gases).

Which body wave arrives after P-waves?

Secondary (S) waves.

Describe S-wave particle motion.

Transverse; particles move up-and-down or side-to-side perpendicular to wave propagation.

Can S-waves travel through liquids?

No; they move only through solids.

Which surface wave causes most damage?

Love waves.

Which surface wave causes most of the shaking people feel?

Rayleigh waves.

What is required to locate an earthquake epicenter using triangulation?

Arrival-time data of P- and S-waves from three different seismic stations.

Define a fault line.

A geological fracture where movement of rock masses has displaced parts of Earth’s crust.

What can rapid movement along a fault produce?

Powerful energy releases that trigger strong earthquakes.

Name two major Philippine fault systems.

Examples: Marikina Valley Fault and Western Philippine Fault (others include Eastern Philippine, Central Philippine, Southern Mindanao, etc.).

What is a mountain belt?

A group of mountain ranges with similar form and origin, usually created by the same orogeny.

How are most mountain belts formed?

By convergence of lithospheric plates at plate boundaries.

Where are earthquake epicenters, active volcanoes, and major mountain belts mainly found?

Along or near lithospheric plate boundaries.

State the Plate Tectonic Theory in brief.

Earth’s lithosphere is broken into moving plates whose interactions create seismicity, volcanism, continental drift, and mountain building.

What is the lithosphere?

The solid, outer part of Earth comprising the crust and uppermost mantle.

What are tectonic plates?

Smaller sections of the lithosphere that move relative to one another.

Define plate boundaries.

Edges where tectonic plates meet and interact.

Why do volcanoes erupt?

Rising magma with lower density and gas pressure reaches the surface, releasing heat and pressure.

How are volcanoes formed?

Magma rises through the crust, erupts as lava and ash, and builds up a volcanic edifice over time.

What qualifies a volcano as "active"?

At least one eruption within the past 10,000 years.

Differentiate erupting and dormant volcanoes.

Both are active; erupting means currently erupting, dormant means quiet now but expected to erupt again.

Give one example of an active Philippine volcano.

Taal, Kanlaon, Bulusan, or Mt. Pinatubo (any one).

Describe the global distribution of active volcanoes.

Mostly along tectonic plate edges, with some intra-plate hotspots such as Hawaii.

Compare thickness of continental and oceanic crust.

Continental crust is thicker (25–70 km) than oceanic crust (7–10 km).

Compare density of continental and oceanic crust.

Oceanic crust is denser (~3.0 g/cm³) than continental crust (~2.7 g/cm³).

What data do scientists use to map plate boundaries?

Locations of earthquakes, active volcanoes, and major mountain ranges.

Name all of Earth’s primary plates. (in order)

Pacific, North American, Eurasian, African, Antarctic, Australian, South American.

Name all of Earth’s secondary plates. (in order)

Examples: Juan de Fuca, Nazca, Cocos, Caribbean, Philippine, Arabian, Indian, Scotian.

List key features of continental lithosphere.

Thick (25–70 km), old, granitic, density ~2.7 g/cm³, found under land masses.

List key features of oceanic lithosphere.

Thin (7–10 km), young, basaltic, density ~3.0 g/cm³, forms ocean floor.

How do P- and S-wave motions differ relative to propagation direction?

P-waves: parallel (compressional); S-waves: perpendicular (shear).

Why are seismograms important?

They allow scientists to determine an earthquake’s location and magnitude.

What is a kinemetric seismograph?

A type of seismograph designed to measure ground motion precisely for earthquake analysis.