Earthquake Hazards and Ground Rupture

Earthquake Hazards

• Ground shaking, the vibratory motion caused by seismic waves, depends on magnitude, depth, epicenter distance, and local geology.

Effects of Ground Shaking

• Structural damage, including collapsed buildings and cracked roads and bridges, can result from ground shaking.
• Infrastructure failure can occur, affecting power, water pipes, and gas lines.
• Ground shaking can trigger other hazards like landslides, liquefaction, and tsunamis.
• Injuries, fatalities, and displacement can be negative impacts on humans.
• The 1990 Luzon earthquake is a key illustration.

Ground Rupture

• Ground rupture involves visible displacement of the Earth's surface due to fault line movement during an earthquake when the fault reaches the surface.

Effects of Ground Rupture

• Breakage of roads, bridges, and pipelines can result from ground rupture.
• Buildings and houses along fault lines are susceptible to damage.
• Ground deformation can occur, rendering areas unsafe for future construction.
• The Marikina Valley Fault System and San Andreas fault are examples of ground rupture.

Liquefaction

• Liquefaction is when loose, water-saturated soil loses strength and behaves like a liquid due to intense shaking, often in areas with loose, fine-grained sediments and a high water table.

Effects of Liquefaction

• Buildings, houses, and roads can sink or tilt due to unstable ground.
• Underground utilities such as pipes, cables, and sewer systems may be displaced or broken.
• Liquefaction can increase flood risk as water is forced to the surface.

Earthquake-Induced Ground Subsidence

• Ground subsidence is the gradual or sudden sinking of the ground due to seismic activity, often caused by the compaction of loose sediments, fault movement, or excessive groundwater extraction.

Effects of Earthquake-Induced Ground Subsidence

• Lowering of land elevation can happen making areas prone to flooding and waterlogging.
• Permanent damage to structures, roads, and farmlands can occur.
• Disruption of drainage systems can lead to long-term environmental changes.

Earthquake-Induced Landslides

• Landslides involve the sudden downward movement of soil, rock, and debris due to ground shaking, usually on steep, unstable slopes.

Effects of Earthquake-Induced Landslides

• Burial of roads, houses, and farmlands can happen due to landslides.
• Blockage of rivers can lead to flooding or landslide dams.
• Landslides can cause loss of lives and destruction of infrastructure.
• Landslides can hit water and generate megatsunamis.
• The deadliest landslide in history happened in China and killed 200,000 people in 675 Big Landslides

Tsunami

• A tsunami is a series of large ocean waves generated by an undersea earthquake, volcanic eruption, or landslide that can travel at speeds up to 800 km/h.

Key Features of a Tsunami

• Tsunamis involve displacement of water from a large event.
• They have much larger wavelengths, up to 120 miles or 200 kilometers.

Natural Warning Signs of a Tsunami

• A strong earthquake near the coast is a natural warning sign of a tsunami.
• Unusual and sudden receding of seawater or sea withdrawal can indicate a tsunami.
• A loud roaring sound from the ocean can be a warning sign of a tsunami.

Effects of Tsunamis

• Massive flooding in coastal areas can result from tsunamis.
• Destruction of homes, roads, and ports can happen due to tsunamis.
• Loss of life due to drowning and strong currents is a major consequence of tsunamis.
• Soil erosion and salinization of agricultural land can occur.

Tsunami Events

• The 2004 Indian Ocean Tsunami caused incalculable damage, with at least 230,000 people killed or missing in 14 countries.
• The 1976 Moro Gulf earthquake and tsunami in Mindanao was a disastrous event causing extreme damage.

Safety Tips for Tsunamis

• Strong or long-lasting ground shaking from an earthquake should trigger a warning.
• A sudden rise or fall of the ocean or an abnormally large wave should trigger a warning.
• A loud roar from the ocean should trigger a warning.

Earthquake Hazard Maps

• Earthquake hazard maps show areas at risk of ground shaking, liquefaction, landslides, and tsunamis.
• They help in disaster preparedness and urban planning.