Earthquake Science: Faults, Waves, Measurement, and Hazards
*EARTHQUAKES:
-in plate boundries bc is where most jaults jostle, collide with, or slide past each other. Also in transform fault zones.
-fault: planar breaks and displacement happens
-fault plane: plane which displacement occurs
*stirke-
Slip
*reverse -> <-
*normal <- ->
-creep: if a displacement is gradual,smooth there is no seismic activity or earthquake (aseismic slip)
-earthquake:is displacement is quick, earthquake happens (seismic slip)
elastic rebound: two slides of the fault snap back elastically to their original place
-epicenter: point on earth’s surface directly above the earthquake focus
-focus: point at which the fault slips
*sharp= deformation is absorbed by asthenosphere’s elasticity
*shallow= lithosphere, more destructive
*SEISMIC WAVES: travel away from the focus
-primary waves= push-pull waves. Compress and expand on a plate aligned with the focus
-secondary waves= shear waves (damaging). Affect the molecular level and perpendicular to the focus.
-Locating the focus= P waves travel faster than S waves. The harder the rock, the faster they travel
-locating the epicenter=
*measuring the effects of an earthquake
–richter scale(ML) measures the magnitude and energy released (cali rock type and crustal formations) measured by a seismograph. No lower upper limits
–moment magnitude (MW) measures magnitude and energy released (world average rock type) measured by a seismograph. Cannot be 1 or 0. Similarities between ML and MW exist in 5-7.
-mercali intensity measures amount of damage to life and property (I nothing felt. II felt only by people. VII difficult to stand. X masonry and frame structures destroyed. XII total destruction)
-affect on humans:
*ground motion: 1995 Kobe, Japan earthquake. Motion= P waves, S waves, elastic rebound, and aftershocks. Same for Haiti
*ground Failure: liquefaction. Not necessarily have to include water.
*tsunami:cause flooding many km from their origin. Can travel at speeds up to 600 miles per hour and great distances.Not associated with tidal action.
*PREDICTING AND FORECASTING:
-earthquake cycle: concept that major earthquakes occur in periodic intervals on given fault zone.
-seismic gap:locked section of an active fault along which few earthquakes occur.May become earthquakes in the future.
-precursors: ground surface may be uplifted. Artificially caused P waves and S wave velocity may drop and rise. Electrical resistivity of rock may increase. Changes in the levels of water wells. Changes in the levels of radon may increase.
–forecasting using the earthquake cycle is reliable, more than precursors. 1. Assume that the stress buildup is primarily associated with the slow movement of lithospheric plates, which will move at specific rate, thus the buildup of sufficient stress to cause a seismic slip at the estimated time. 2. The particular physical properties of rocks along a specific fault are reliable enough to know how much energy can be accumulated before a seismic slip occurs.
-controlling: 1. Unlocking faults- by artificial shocks produced by specially placed nuclear devices. Not used because radiation is released. Too little is know about the size of the charge and where to place it, it might unlock a catastrophe. 2. Lubricating faults or fluid injection- into the fault slip area can perpetuate minor slippage and stave off the large accumulation of energy. Proven results from injected waste disposal, injection of fluids (ferromagnesium clays). The quantity of injection is limited (fault without water has too much friction for it to move; fluid help the fault to move). 3. Population response threats remains lackadaisical.