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Earthquake Basics

• An earthquake happens when rocks release stored elastic energy, causing sudden ground movement and seismic waves.

Causes of Earthquakes

• Earthquakes can occur due to the sudden release of energy along fault lines.
• Volcanic activity causes earthquakes.
• Other causes are human activities, like mining.

Parts of an Earthquake

• The focus or hypocenter, is the point beneath the Earth's surface where an earthquake starts and seismic waves originate.
• The epicenter is the point on the Earth's surface directly above the focus.
• A fault plane occurs as a surface where the slip or displacement occurs during an earthquake.
• Seismic waves are energy waves that start from the focus and shake the ground.
• Aftershocks are smaller earthquakes that happen after the main shock, usually in the same area.

Types of Faults

• Normal faults are caused by tension and pull the Earth's crust apart.
• Reverse (thrust) faults are caused by compression and push the Earth's crust together.
• Strike-slip faults are caused by shear stress and slide plates horizontally past each other.

Seismic Waves

• Seismic waves comprise P-waves and S-waves.

Body Waves

• Primary Waves (P-Waves) are the fastest seismic waves.
• P-waves travel through solids, liquids, and gases, exhibiting a push-pull, compressional motion.
• Secondary Waves (S-Waves) are slower than P-waves.
• S-waves only travel through solids.

Surface Waves

• Surface waves comprise love waves and rayleigh waves.
• Love waves move the ground side-to-side, named after Augustus Edward Hough Love.
• Rayleigh waves exhibit a rolling motion similar to ocean waves, are is named after Lord Rayleigh.

Potential Earthquake Hazards

Ground Shaking

• Ground Shaking is a direct result of seismic waves.
• It can cause buildings and structures to collapse.

Ground Rupture

• A Ground rupture occurs when the Earth's surface breaks along a fault line.
• Ground rupture usually appears along zones of weakness.

Liquefaction

• Liquefaction is when saturated soil loses strength and behaves like a liquid.
• Common indications include water leaking from the ground.

Ground Subsidence

• Refers to a downward sinking or settling of the ground surface.

Tsunami

• A tsunami is a series of giant waves caused by underwater disturbances.

Stages of Tsunami Formation

• Initiation is the displacement of ocean water which triggers wave formation.
• Waves split into distant and local tsunamis.
• Amplification means wave heights increase as they approach shore.
• Runup is when waves hit the shore with accumulating force.

Impending Tsunami Signs

• Ground shaking near a body of water may indicate an impending tsunami.
• Unusual sea-level changes can be a sign (receding shoreline).
• Rumbling sounds from incoming waves.

Landslides

• Landslides involve the downward movement of rock, debris, or earth on slopes.
• Earthquakes can trigger landslides.

Factors Influencing Landslides

• Steep slopes can lead to landslides.
• Weak slope materials.
• Rock weathering increases the risk of landslides.
• Overloading on slopes causes landslides.

Measuring Earthquakes

• Magnitude measures the energy released at the source of the earthquake.
• It is quantified using scales like the Richter or Moment Magnitude Scale.
• Intensity measures the effects and how strong the shaking feels at specific locations.
• It is typically measured using the Modified Mercalli Intensity (MMI) scale.

Earthquake Preparedness (PHIVOLCS Guidelines)

• Steps to take: Develop an emergency plan.
• Steps to take: Secure heavy furniture and appliances.
• Steps to take: Prepare an emergency kit with essentials.
• Steps to take: Participate in earthquake drills.
• Stay informed with official alerts and warnings.

Volcano Introduction

• A volcano is an opening in the Earth's surface through which molten rock (magma), volcanic gases, ash, and other materials are ejected.
• Volcanoes form when magma from beneath the Earth's crust rises to the surface.
• Volcanoes often show around tectonic plate boundaries or over hotspots.

Volcano Parts

• Magma Chamber is the underground reservoir where magma accumulates.
• Vent is the opening through which magma, gas, and ash escape to the surface.
• Crater is the bowl-shaped depression at the summit of the volcano.
• Caldera is the large depression formed when a volcano collapses after an eruption.
• Conduit (Pipe) is the pathway for magma to travel from the chamber to the surface.
• Lava Flow is the stream of molten rock that pours out during an eruption.
• Ash Cloud is the cloud of volcanic ash and gases released into the atmosphere.
• Flank is the side of the volcano where secondary vents can form.

Volcano Classification by Composition/Structure

• Shield Volcanoes have broad, gently sloping sides.
  • They are built from low-viscosity basaltic lava.
  • Example: Mauna Loa (Hawaii).
• Stratovolcanoes (Composite Volcanoes) have a steep, conical shape with alternating layers of lava and pyroclastic material.
  • Eruptions are explosive.
  • Example: Mount Fuji (Japan), Mount Mayon (Philippines).
• Cinder Cone Volcanoes are steep-sided, small volcanoes formed from pyroclastic fragments.
  • Eruptions are short-lived.
  • Example: Paricutin (Mexico).
• Lava Domes are formed from slow-moving, viscous lava.
  • Collapses can cause pyroclastic flows.
  • Example: Mount St. Helens Lava Dome (USA).

Volcano Classification by Activity

• Active Volcanoes are currently erupting or showing signs of unrest.
• Dormant Volcanoes are not currently erupting but could erupt in the future.
• Extinct Volcanoes no longer have a magma supply and are not expected to erupt.

Volcano Hazards

Lahar (Volcanic Mudflow)

• Rapid flows of water-saturated volcanic debris.
• The flow is triggered by rain, melted ice, or crater lake breaches.
• These can bury communities and infrastructure.

Ashfall (Tephra Fall)

• Volcanic ash ejected into the atmosphere settles over large areas.
• Hazards: respiratory issues, contaminated water, machinery damage, and roof collapse.

Pyroclastic Flow

• Fast-moving, hot mixtures of gas, ash, and volcanic rock.
• Speeds up to 700 km/h and temperatures over 800°C.
• It is highly destructive to life and property.

Ballistic Projectiles

• Large volcanic rocks ejected during explosive eruptions.
• These travel several kilometers from the volcano.

Volcanic Gas

• Emissions include CO2, SO2, and H2S.
• The gasses can cause respiratory problems, acid rain, and fatalities in high concentrations.

Lava Flow

• It is streams of molten rock that destroy everything in their path.
• Flows are usually slow-moving but cause irreversible damage.

Impending Eruption Signs

• Increased Seismic Activity: More frequent volcanic earthquakes indicating rising magma.
• Ground Deformation: Swelling or sinking of the volcano's surface.
• Gas Emissions: Elevated release of volcanic gases like SO2 and CO2.
• Changes in Temperature: Rising temperatures around the crater or vents.
• Small Steam or Ash Explosions: Precursors to a larger eruption.
• Unusual Animal Behavior: Animals may flee the area before an eruption.

Monitoring and Early Warning Systems

• Ground Deformation Monitoring: Detects changes indicating magma movement.
• Seismic Activity Monitoring: Tracks earthquakes and volcanic tremors.
• Gas Emission Studies: Monitors changes in volcanic gas output.
• Remote Sensing and Satellite Imaging: Provides continuous observation of volcanic activity.

Preparedness and Mitigation Strategies

• Develop hazard maps and identify at-risk zones.
• Establish evacuation routes and exclusion zones.
• Conduct community education and regular drills.
• Strengthen structures to withstand ashfall and lahars.
• Use early warning systems to alert communities.

Significant Volcanic Events

• Mount Pinatubo (1991, Philippines) involved a massive eruption with global climatic effects.
• Mount St. Helens (1980, USA) had pyroclastic flows and significant property damage.
• Krakatoa (1883, Indonesia) triggered devastating tsunamis and global temperature drop.

Health and Environmental Impacts

• Respiratory issues from ash inhalation.
• There are also contaminated water sources and agricultural damage.
• Long-term climate effects due to volcanic aerosols.

Electric Flux

• Electric flux measures the number of electric field lines passing through a given surface.
• Formula: Φ = E ⋅ A ⋅ cos(θ), where E is electric field strength (N/C), A is the area of the surface (m²), and θ is the angle between the electric field, and the normal to the surface.
• Maximum flux occurs when the surface is perpendicular to the field (θ = 0°).
• Zero flux occurs when the surface is parallel to the field (θ = 90°).

Importance of Electric Flux

• Describes how electric fields interact with surfaces.
• Helps calculate the strength of the field passing through an area.

Gauss's Law

• Gauss's Law relates the electric flux through a closed surface to the charge enclosed.
• Formula: Φ = Qenc/ε0, where Qenc is the total charge enclosed (C) and ε0 is the permittivity of free space (≈ 8.85 × 10-12 C²/N⋅m²).

Gaussian Surfaces

• Spherical: best for the use of point charges and spherical charge distributions.
• Cylindrical: Used for determining line charges.
• Planar: Used for the determination of infinite plane charges.

Gauss's Law Applications

• Calculating electric fields for symmetric charge distributions.
• Understanding charge distribution on conductors.

Electric Potential Energy (U)

• Energy stored due to the position of a charge in an electric field.
• Formula: U = k(q1q2)/r, where k is Coulomb's constant (8.99 × 10^9 N⋅m²/C²), q1 and q2 are charges (C), and r is the distance between charges (m).
• Positive U: Like charges repel, with work needed to bring them together.
• Negative U: Opposite charges attract, releasing energy when they come closer.
• Moving a charge in an electric field requires work, changing the system's potential energy.

Electric Potential (V)

• Electric potential is the potential energy per unit charge.
• V = U/q = k(q)/r
• Unit: Volt (V) = Joule/Coulomb (J/C).
• Scalar quantity
• Zero potential is at infinity.
• High potential near positive charges; low near negative charges.

Potential Difference (Voltage)

• Work done in moving a unit charge between two points.
• ΔV = W/q

Relationships and Applications

• Electric field (E): Gradient of the electric potential (E = -dV/dr).
• Potential energy (U): Related to potential by U = qV.
• Flux and Gauss's Law: Connect field lines to charge distribution.
• Practical: design of capacitors, insulation, and shielding in electrical systems, and analyzing electric fields around conductors.

Summary

• Electric Flux: Measures field lines through a surface.
• Gauss's Law: Relates flux to enclosed charge.
• Electric Potential Energy: Energy due to charge position.
• Electric Potential: Energy per unit charge; measured in volts. These concepts are interrelated and vital for understanding electrostatics.