3. EARTHQUAKESEARTHQUAKES
DEFINITIONS
Earthquake- the vibration of the ground due to the sudden release of
energy accumulated in a deformed rock
Focus (Hypocenter)- spot underground where the rock begins to break-
point at which slip initiates
Epicenter- the point on the land surface directly above the focus
Aftershock- tremors that occur as rocks adjust to their new position
Seismology- the study of earthquake
4. SEISMIC WAVESSEISMIC WAVES
Earthquake’s energy is transmitted through the earth as seismic
waves
oTwo types of seismic waves radiate from the focus
oBody waves- transmit energy through earth’s interior Primary (P)
wave- rocks vibrate parallel to direction of wave (v=4-7km/sec)
oCompression and expansion (slinky example)
oSecondary (S) wave- rocks move perpendicular to wave direction
(v=2-5 km/sec)
oRock shearing (rope-like or ‘wave’ in a stadium) S-wave cannot
travel through liquid
oSurface waves- transmit energy along earth’s surface
oLove (L) wave- Rock moves from side to side like snake
oRaleigh ® wave- Rolling pattern like ocean wave
5. LOCATING & MEASURINGLOCATING & MEASURING
EARTHQUAKEEARTHQUAKE
• Seismometer- instruments that detect seismic waves
• Seismograph- device that measures the magnitude of
earthquake
• seismogram is visual record of arrival time and
magnitude of shaking associated with seismic wave
• Mercalli Intensity scale
•Measured by the amount of damage caused in human terms- I (low) to
XII (high)
• Richter Scale- (logarithmic scale)
•Magnitude- based on amplitude of the waves
•Earthquake total energy- uses moment magnitude scale
6. LOCATING EPICENTER &LOCATING EPICENTER &
FOCUS DEPTH (EQ CLASSIFICATIONFOCUS DEPTH (EQ CLASSIFICATION))
• Use Arrival time at a recording station (time lag between P & S
waves) to locate the epicenter of an earth quake
• Need three stations to determine the epicenter
• Maximum Depth of Focus
• Shallow focus EQ < 70 km (45 mi) most earthquakes
• Intermediate focus EQ- 70-300 km (45- 180 mi)
• Deep focus EQ- > 300 km (> 180 mi)
7. Earthquake LocationsEarthquake Locations
• Most EQs occur in the circum pacific
region
• 80% of shallow focus EQ; 100% of deep focus
EQ
• Most EQs occur along plate boundaries
• Oceanic trenches, Benioff zones,
Mediterranean- Himalayan
• Most EQs in US occur near the west coast
• San-Andreas Fault
8. EFFECTS OF EARTHQUAKESEFFECTS OF EARTHQUAKES
• Ground Displacement
• Lateral and vertical
• Landslides
• Liquefaction
• Conversion of formally stable fine grain materials to a fluid mass
• Seiches
• The back & forth movement of water in a semi-closed/closed body of
water- could cause flooding
• Tsunamis-
• more from submarine landslide
• Fire
11. COPING WITH EARTHQUAKECOPING WITH EARTHQUAKE
• Earthquake zone
• Plate boundaries
• Assessing local seismic history and future risks
• Land use planning
• Quake reinforcement of building/structures
• Short term and Long term forecast
• Contingency plan
