Copyright © by Isiorho1 Earthquake Slides By Dr. S. A. Isiorho

Copyright © by Isiorho2 Earthquakes 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

Copyright © by Isiorho3 Seismic Waves Earthquake’s energy is transmitted through the earth as seismic waves  Two types of seismic waves radiate from the focus  Body waves- transmit energy through earth’s interior  Primary (P) wave- rocks vibrate parallel to direction of wave (v=4- 7km/sec)  Compression and expansion (slinky example)  Secondary (S) wave- rocks move perpendicular to wave direction (v=2-5 km/sec)  Rock shearing (rope-like or ‘wave’ in a stadium) S-wave cannot travel through liquid  Surface waves- transmit energy along earth’s surface  Love (L) wave- Rock moves from side to side like snake  Raleigh ® wave- Rolling pattern like ocean wave

Copyright © by Isiorho4 Locating & Measuring Earthquake  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

Copyright © by Isiorho5 Locating Epicenter & Focus 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 km ( mi)  Deep focus EQ- > 300 km (> 180 mi)

Copyright © by Isiorho6 Richter Scale  Richter scale is based on a log scale, meaning that each subsequent number is ten times more in amplitude of vibration- this translates to about 30 times more energy than the previous number.  Example: an EQ of 5.0 is 10 times greater than an EQ of 4.0 on the Richter scale and is 30 times more in energy. An EQ of 5.0 is 100 times greater in amplitude than an EQ with 3.0 reading on the Richter scale

Copyright © by Isiorho7 Earthquake 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

Copyright © by Isiorho8 Effects 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

Copyright © by Isiorho9 Coping 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