Lecture 10: Earthquakes

• what is an earthquake?

  faults in earths crust get locked up, due to friction and then released.
• Fault Plane: the area that ruptures, can cover 1000s km
• Focus/Hypocentre: where the ruptures starts on the fault plane.
• Epicentre: the pint on the earths surface directly above the focus.
• how deep are shallow EQ?

  0-70km thick
• what plate boundary are shallow EQ?

  constructive and conservative.
• How deep are intermediate EQ?

  70-300km deep
• how deep are deep EQ?

  300-700km
• Seismographs: measure ground displacement, velocity or acceleration vs time.
• Body Waves: primary wave, compressional, parallel.
• S Waves: shear waves, perpendicular.
• seismic moment: determined by the magnitude of the force which acts on earths lithosphere.
• Strength/Intensity depends on?


  magnitude, distance, focal depth, ground type.
• Primary effect of EQ: fault rupture and ground shaking
• Fault/Surface Rupture: horizontal or vertical displacement across a ruptured fault.
• a shallow focus can allow the rupture to break through the earths surface, causing ground deformation.
• Ground Shaking: due to rapid ground acceleration, main cause of damage to buildings.
• Ground Liquefaction: a solid medium turns into fluid medium due to shaking.
• soils prone to liquefaction are sandy, silty, gravelly and water saturated.
• tsunamis: occur where fault movement in the vertical plane offshore leads to a sudden vertical change in the seabed.
• EQ RISK= Hazard Level x Exposure x Vulnerability.
• vulnerability- preparedness and resilience to volcanic disasters.
• Reducing Vulnerability- EQ Hazard Assessment: forecasting informs land use, building regulation, insurance.
• Reducing Vulnerability- Land-Use Planning: based on seismic hazard maps. avoid areas of high hazard risk.
• Reducing Vulnerability- Anti-seismic Design: retrofitting, cross braing, hi-tech engineering, building codes.
• Reducing Vulnerability- Education, Training, Emergency Planning: preparedness, emergency training, rapid mobilisation of emergency and medical services.