DRRGP2 REVIEWER

Earthquake Basics

• Ground movement happens suddenly, caused by the release of elastic energy stored in rocks
• Generates seismic waves

Causes of Earthquakes

• Sudden release of energy occurs along fault lines
• Earthquakes can result from volcanic activity
• Human activities, e.g., mining or building reservoirs, can cause seismicity

Parts of an Earthquake

• The focus (hypocenter) is the point within the Earth where the earthquake starts and source of seismic waves
• The epicenter is the point on Earth's surface directly above the focus
• A fault plane refers to the surface where the slip or displacement happens
• Energy waves radiate from the focus, causing the ground to shake
• Smaller earthquakes that follow the main shock and occur in the same area

Types of Faults

• Normal faults come from tension pulling the crust apart
• Reverse (thrust) faults come from compression pushing the crust together
• Strike-slip faults come from shear stress, where plates slide horizontally

Seismic Waves

Body Waves

• Primary waves (P-waves) are the fastest seismic waves
• P-waves travel through solids, liquids, and gases
• They have a push-pull (compressional) motion
• Secondary waves (S-waves) move slower than P-waves
• S-waves only travel through solids with a side-to-side (shear) motion

Surface Waves

• Love waves move the ground side-to-side
• Rayleigh waves have a rolling motion like ocean waves

Potential Earthquake Hazards

Ground Shaking

• Ground shaking results directly from seismic waves
• It can cause buildings and structures to collapse

Ground Rupture

• Ground rupture happens when the Earth's surface breaks along a fault line and is common in zones of weakness

Liquefaction

• Saturated soil loses strength and acts like a liquid
• Common signs include water leaking from the ground

Ground Subsidence

• Downward sinking or settling of the ground surface

Tsunami

• Tsunamis are series of giant waves caused by underwater disturbances

Stages of Tsunami Formation

• Initiation starts with the displacement of ocean water that triggers wave formation
• Split involves waves splitting into distant and local tsunamis
• Amplification happens as wave heights increase when they approach the shore
• Runup is when waves hit the shore with accumulating force

Signs of an Impending Tsunami

• Ground shaking near a body of water

• Unusual sea-level changes, such as a receding shoreline

• Rumbling sounds come from incoming waves

Landslides

• The downward movement of rock, debris, or earth on slopes is triggered by earthquake shaking

Factors Influencing Landslides

• Steep slopes
• Weak slope materials
• Rock weathering
• Overloading on slopes

Measuring Earthquakes

Magnitude

• Measures the energy released at the earthquake's source, quantified using scales like the Richter or Moment Magnitude Scale

Intensity

• Measures the effects and how strong the shaking is felt at specific locations
• Commonly measured using the Modified Mercalli Intensity (MMI) scale

Earthquake Preparedness (PHIVOLCS Guidelines)

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

Introduction to Volcanoes

• A volcano is an opening in the Earth's surface
• Molten rock or magma, volcanic gases, ash, and other materials are ejected
• Volcano comes from magma rising from beneath the Earth's crust to the surface
• Often occurring where tectonic plates meet or over hotspots

Parts of a Volcano

• The magma chamber is an underground reservoir where magma accumulates
• The vent is an opening where magma, gas, and ash escape
• The crater is a bowl-shaped depression at the volcano's summit
• A caldera is the large dip that forms when a volcano collapses after eruption
• The conduit (pipe) is the pathway allowing magma to travel from the chamber to the Earth's surface
• Lava flow is a stream of molten rock during an eruption
• Ash clouds contain volcanic ash and gases released into the atmosphere
• The flank is the side of the volcano where secondary vents can form

Classification of Volcanoes

By Composition and Structure

• Shield volcanoes feature broad and gently sloping sides, built from low-viscosity basaltic lava
• Stratovolcanoes (composite volcanoes) have a steep, conical shape with layers of lava and pyroclastic material with explosive eruptions
• Cinder cone volcanoes are steep-sided, small volcanoes made of pyroclastic fragments with short-lived eruptions
• Lava domes are formed from slow-moving, viscous lava
• They can collapse and cause pyroclastic flows

By Activity

• An active volcano is currently erupting or showing signs of unrest
• A dormant volcano isn't currently erupting but could erupt later
• Extinct volcanoes have no longer magma supply and are not expected to erupt

Volcano Hazards

Lahar (Volcanic Mudflow)

• Rapid flows contain mix of water-saturated volcanic debris
• It's triggered by rain, melted ice, or crater lake breaches, and they can bury communities and infrastructure

Ashfall (Tephra Fall)

• Loose or hardened volcanic ash ejected high up that settles over large areas with hazards such as respiratory issues, contaminated water, machinery damage, and roof collapse

Pyroclastic Flow

• Fast-moving, hot mixtures containing gas, ash, and volcanic rock, with speeds up to 700 km/h and temperatures over 800°C
• The destructive force will be destructive to life and devastate property

Ballistic Projectiles

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

Volcanic Gas

• Emissions include CO2, SO2, and H2S
• Resulting in respiratory problems, acid rain, and fatalities in high concentrations

Lava Flow

• Molten rock streams destroy everything in their path
• Slow-moving but cause irreversible damage

Signs of an Impending Eruption

• Increases in the number of volcanic earthquakes indicates rising magma
• The ground will deform- swelling or sinking of the volcano surface
• Gas emissions will increase in the release of volcanic gases, like SO2 and CO2
• The temperature rises around the crater or vents
• Small steam or ash explosions might be precursors to a larger eruption
• unusual animal behaviour- 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 both earthquakes and volcanic tremors
• Gas missions 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 the structures to withstand ashfall and lahars
• Use early warning systems to alert communities

Case Studies of Significant Volcanic Events

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

Health and Environmental Impacts

• Respiratory issues occur from ash inhalation
• There is contaminated water sources and agricultural damage
• Long-term climate effects come from volcanic aerosols

Electric Flux

Definition

• Measures the electric field lines passing through a given surface.
• Formula: Φ = E · A · cos(θ), where E is the electric field strength, A is the area of the surface, 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

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

Gauss's Law

Definition

• This relates the electric flux through a closed surface to the charge enclosed.
• Formula: Φ = Q_enc/ε₀, where Q_enc is the total charge enclosed and ε₀ is the permittivity of free space (≈ 8.85 × 10⁻¹² C²/Nm²)

Electric Potential Energy (U)

Definition

• Energy stored due to the position of the charge in an electric field. * Formula: U = k(q1q2)/r, where k is Coulomb's constant (9 × 10⁹ N·m²/C²), q1, q2 are charges, and r is the distance between charges.
• Field does positive work on charge. U decreases
• Field does negative work on charge. U increases.

Electric Potential (V)

Definition

• This is the potential energy per unit charge.

Formula

• V = U/q = k(q)/r, with a unit of Volt (V), equal to a Joule/Coulomb (J/C)
• Scalar Quantity
• Zero potential at infinity
• High potential near positive charges; low near negative charges

Relationships and Applications

• Relationship Between Concepts: Electric field (E) comes from the gradient of the electric potential (E = -dV/dr)
• Potential energy (U) comes from related to potential by U = qV
• Practical Applications include designing capacitors, insulation and shielding in electrical systems, and analyzing electric fields around conductors

Summary

• Electric Flux is a measurement of field lines through a surface.
• Gauss's Law relates flux to enclosed charge
• Electric Potential Energy is the energy due to charge position
• Electric Potential is the energy per unit charge
• Measured in volts. Concepts are interconnected, fundamental to understanding electrostatics

Concept of Potential Difference

• Electric Potential (V) is the electric potential at a point
• Also the work done to bring with a unit positive charge from infinity (zero potential energy) to that point
• Key Point: Potential difference doesn't depend on of the path taken