Earthquake Formation and Faults

• The preliminary activity involves laying a ruler on a table with ¾ of its length over the edge, bending the free end, and observing its movement.
• The activity is to explore what happens to energy when bending the ruler, what happens to released energy, if vibration occurse and how it relates to earthquakes.

Earthquake Formation

• Earthquakes occur when the Earth's rocks are deformed by pushing and pulling forces.
• The energy released when rock layers break is manifested as earthquakes, causing violent shaking or movement of the ground.
• Earthquake energy travels through the Earth's solid and liquid materials as vibrations, known as seismic waves.
• Earthquakes can result from sudden movements along faults, plate boundaries, or volcanic eruptions.

Faults and Earthquakes

• Faults are cracks in the ground or breaks in rock where the surfaces rub against each other.
• Faults are soft, weak, and unstable spots on the Earth's ground
• Fault movement occurs when tectonic plates shift and separate.
• Earthquakes happen when rocks break due to stress.

Plate Boundaries

• Plate boundaries are areas or regions between two tectonic plates.
• Tectonic plates are large pieces of the lithosphere, with continents sitting on top.
• Movement occurs along plate boundaries, especially where faults exist.

Types of Earthquakes

• Tectonic earthquakes are caused by faults and the movement of plate boundaries.
• Volcanic earthquakes are induced by rising lava or magma within a volcano.

Philippines and Earthquakes

• The Philippines is prone to earthquakes due to its location within the Pacific Ring of Fire.
• The Pacific Ring of Fire is a region encircling the Pacific Ocean's rim, home to over 70% of the world's active volcanoes, both on land and underwater.
• The Pacific Ring of Fire is known for its tectonic plates being actively move.

Earthquake Anatomy

• The focus or hypocenter is the point of origin of seismic waves.
• The epicenter is the point on the Earth's surface directly above the focus.
• The fault plane is within the Earth's interior where the rocks slip during an earthquake.

Active vs Inactive Faults

• Active faults have moved within the last 10,000 years and may move again.
• Inactive faults are fractures with no geologic activity in the last 10,000 years, though they may reactivate.

Measuring Earthquakes

• Earthquakes vary in strength, and the terms intensity and magnitude describe the size and shaking caused by an earthquake.
• Seismology is the study of earthquakes.
• A seismologist specializes in studying earthquakes and their effects.

Earthquake Intensity

• Intensity refers to the perceptible strength of an earthquake in a specific area.
• It describes the effects and damage caused by earthquakes to people, objects, infrastructures and land surfaces.
• Intensity provides a descriptive measure of an earthquake's strength.
• In 1996, PHIVOLCS adopted a 10-point intensity scale, the PHIVOLCS Earthquake Intensity Scale (PEIS), replacing the Rossi-Forel scale.
• PEIS categorizes earthquakes from scarcely perceptible (I) to completely devastating (X).
• Earthquake proximity is generally greater near the epicenter.
• Variations in intensities can occur in two nearby areas.
• Factors affecting the intensity or shaking of an earthquake: depth, fault rupture distance, ground material, and building construction.

Magnitude

• Magnitude is the quantitative measure of an earthquake's strength.
• Magnitude refers to the amount of energy released, determined from the amplitude of surface waves. -A seismograph or seismometer detects and records ground motions from earthquakes and eruptions.
• A seismogram is the recording of an earthquake.

Richter Scale

• The Richter Scale measures earthquake magnitude quantitatively.
• The Richter Scale was a scale created by American Seismologist Charles Francis Richter.
• The Richter Scale is a logarithmic scale where each unit increase equals a roughly tenfold increase in measured amplitude.
• Energy released by earthquakes increases by about 30 times with each scale step.

Seismic Waves

• Seismic waves are formed or generated during earthquakes.

Body Waves

• Body waves travel through the Earth's interior and have a higher frequency than surface waves. -P-waves (Primary waves) also known as pressure waves, travel through solid and liquid materials.
• P-waves move quickly, reaching the seismograph first, propagating by compressing and expanding substances, with particle velocity parallel to wave direction.
• S-waves (Secondary waves) known as shear waves, and can only propagate in hard, solid materials by vibrating particles perpendicular to propagation.
• S-waves cannot spread across a liquid.
• Seismologists verified the liquid outer core of the Earth by tracking S waves.

Surface Waves

• Surface waves flow along the Earth's surface-air boundary and have a lower frequency than body waves.
• Surface waves responsible for earthquake damage, have particles that move in a circular or elliptical pattern.
• Surface wave strength decreases deeper below the surface.
• Rayleigh waves, named after Lord Rayleigh, are a mix of longitudinal, compressional, and dilatation motions, particles travel elliptically in the vertical plane.
• Rayleigh are dispersive, amplitudes decline exponentially with depth.
• Love Waves particles jerk back and forth perpendicular to wave transmission, motion is horizontal.
• Love wave energy radiates in two directions, with amplitude diminishing depth.

Earthquake Hazards

• Earthquake hazards depend on the earthquake's strength and the affected area's physical features.

Primary Earthquake Hazards

• Groundshaking is the main cause of destruction.
• Liquefaction is when materials and soil lose strength and behave like liquid.
• Landslides are downward movements of soil or rock, from ground shaking.
• Ground rupture is ground deformation along existing faults.
• Tsunamis are ocean waves generated by underwater earthquakes or volcanic eruptions, also called "harbor waves" in Japanese.