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WHAT IS AN EARTHQUAKE?• intense ground shaking caused by sudden release of energy• can be generated by bomb blasts, volcanic eruptions and sudden slippage along faults• a geologic hazard for those living in earthquake- prone areas• also provided valuable information about the Earth’s interior
EARTHQUAKE MAGNITUDE SCALE Magnitude Earthquake Effects Estimated Number Each Year 2.5 or less Usually not felt, but can be 900,000 recorded by seismograph. 2.5 to 5.4 Often felt, but only causes 30,000 minor damage 5.5 to 6.0 Slight damage to buildings 500 and other structures 6.1 to 6.9 May cause a lot of damage 100 in very populated areas. 7.0 to 7.9 Major earthquake. Serious 20 damage. 8.0 or greater Great earthquake. Can One every 5 to 10 totally destroy communities years near the epicenter.
for each whole number you go up on the Richter scale, theamplitude of the ground motion recorded by a seismographgoes up ten times.Using this scale, a magnitude 5 earthquake would result in tentimes the level of ground shaking as a magnitude 4 earthquake(and 32 times as much energy would be released).To give you an idea how these numbers can add up, think of itin terms of the energy released by explosives: a magnitude 1seismic wave releases as much energy as blowing up 6 ouncesof TNT. A magnitude 8 earthquake releases as much energy asdetonating 6 million tons of TNT. TNT
DESCRIBING THE STRENGTH OF AN EARTHQUAKE Intensity is the degree of ground shaking at a given locale based on the amount of damage Depends on distance to earthquake & strength of earthquake Modified Mercalli Intensity ScalePhilippine Earthquake Intensity Scale Magnitude is calculated from seismic records and estimates the amount of energy released at the source Depends on size of fault that breaks Richter Scale
INTENSITY OF AN EARTHQUAKEPhilippine Earthquake Intensity Scale – I to X (PHIVOLCS)
STRUCTURAL DAMAGE DUE TO EARTHQUAKE VIBRATIONS DEPENDS ON: Wave amplitudes Duration of vibrations Nature of material upon which the structure rests Design of structure
Earthquake Destruction important factors:Nature of material uponwhich structure restsA building on bedrock experiencesless movement compared to astructure built on looselyconsolidated sediments (tend toamplify shaking)
Earthquake Destructionimportant factors: Intensity & duration of shaking Mexico City, 1985
Earthquake Destructionimportant factors: Building design :
EARTHQUAKE PREDICTION: SHORT TERM• Monitor to look for patterns of recurrence• Strange animal behavior• Increase in seismic tremors (mini-quakes)• Seismic gaps• Gas emissions• Electromagnetic signals
drill a deep hole in order to install instruments directly within the San Andreas Fault Zoneelectronic laser, ground movementmonitoring system in California to study the San Andreas Fault seismograph seismic sensor