Seismic Activity and Earthquake Hazards

Industrial Seismic Activity

• Industrial activities like geothermal energy production, fracking, and wastewater disposal can increase seismic activity.
• Faults with recent displacements are classified as "active".

Types of Faults

• Left lateral strike-slip fault
• Right lateral strike-slip fault
• Thrust fault (compressional stress)
• Reverse fault (compressional stress)
• Normal fault (extensional stress)
• Blind thrust fault

Earthquake Hazards

• Ground shaking
• Ground rupture
• Liquefaction
• Earthquake-induced ground subsidence
• Tsunami

Ground Shaking

• Energy from the focus/hypocenter is transmitted as seismic waves
• Earthquake intensity depends on wave velocity
• P-waves (compressional waves) are the first to arrive and cause high-frequency vibrations
• S-waves (shear waves) are the second to arrive and vibrate side-to-side
• Surface waves (Rayleigh and Love waves) are the last to arrive and cause low-frequency vibrations
• P-waves and S-waves primarily affect low structures due to high-frequency vibrations
• Surface waves affect taller structures due to low-frequency vibrations

Ground Rupture

• Ground moves and breaks due to tension/cracks
• Common in areas along fault lines, called "zones"

Liquefaction

• Water-saturated land experiences liquefaction when the ground shakes
• Ground shaking causes grains to loosen, creating liquid-like soil

Earthquake-Induced Ground Subsidence

• The ground sinks
• Can be man-made by overpumping groundwater

Tsunami

• A series of waves in a wave train generated by sudden vertical displacement of a water column

Earthquake Facts

• Earthquakes are measured on the Richter scale (1 being the weakest, 10 being the strongest).
• The power of an earthquake is measured using a seismometer.
• The focus is the point inside the Earth's crust where the earthquake originates.
• Energy released from an earthquake travels in seismic waves
• The epicenter is directly above the focus on the Earth's surface.

Earthquake Components

• Hypocenter/Focus: Primary source force underneath the ground
• Epicenter: Point on the surface parallel to the focus

Driving Forces of Earthquakes

• Tectonic movement: Plates move due to pressure driven by convection
• Volcanic activity: Volcanically-caused long-period earthquakes are produced by vibrations generated by volcanic activity.

Man-Made Earthquakes

• Humans can induce earthquakes through activities such as fracking and wastewater disposal