Hazards - Seismic Hazards Flashcards
What three ways are earthquakes measured?
1) Richter Scale.
2) Moment Magnitude Scale (MMS).
3) Mercalli Scale
How does the Richter Scale measure earthquakes?
Logarithmic scale e.g. magnitude 6 is 10x more powerful than 5 and 100x more powerful than 4. Major events measure above 7. Standardized measurements allows for easy comparison but less accurate for categorizing medium to large earthquakes.
How does the Moment Magnitude Scale measure earthquakes?
Based on total amount of energy released. Also logarithmic with no upper limit. More accurate than Richter for larger earthquakes but less accurate for smaller ones.
How does the Mercalli Scale measure earthquakes?
Based on observed impact of event by reports and photographs. Recorded in roman numerals 1-12. (I) Instrumental being detected only by seismographs, (V) Rather Strong awakening sleeping people and felt by those walking around, (XII) Catastrophic being total destruction. More descriptive yet subjective and limited to urban setting.
What are the hazards of body waves?
P waves are the fastest, moving through land and liquid, pushing and pulling, longitudinal.S waves are slower and only move through solid rock, up and down or side-to-side, transverse.
What are the hazards of surface waves?
Love waves move fast along surface, side-to-side. Rayleigh waves move in a circular rolling motion like the ocean across surface.
What are the hazards of tsunamis?
Large waves caused by displacement of water in the ocean. Greater movement of sea floor, the greater volume of water displaced. More powerful the closer the epicenter is to the coast due to waves losing less energy. Huge wavelengths and small wave height in open sea yet dramatically increases upon hitting coast creating powerful wall of water.
What are the hazards of landslides?
Shaking dislodges material causing it move downslope quickly.
What is the hazard of liquefaction?
Soil is saturated with water and shockwaves cause it to act like a liquid and consequently subside if heavy weight lies on top such as buildings.
How is a seismometer used to predict seismic acitivity?
Receives shockwaves and plots data on seismogram. Foreshocks are small scale earthquakes often predating larger earthquakes.
How is the water table level used to predict seismic activity?
Microcracks created by stress caused by tectonic activity which water percolates into, lowering the groundwater level. Water table rises again before event.
How is a radon gas sensor used to predict seismic activity?
Radon is a radioactive decay product of uranium in granite which cracks with building pressure of oncoming earthquake. If traces are seen to increase it means new cracks are forming.
How is remote sensing used to predict seismic activity?
Satellites survey changes in plate movement and minute changes in Earth’s crust with high accuracy.
How are strain gauges used to predict seismic activity?
Measure and record stretching and compression of Earth’s crust due to shockwaves.
How is preparedness used in response to seismic hazards?
1) Earthquakeand tsunami warning systems implemented.
2) Education of the public about evacuation and how to shelter effectively.
3) Land-use planning to identify areas at risk.
How is mitigation/adaptation used in response to seismic hazards?
1) Buildings constructed to withstand earthquakes and be shake-proof/shock-absorbent or retro-fit older buildings.
2) Smart meters cut off gas and electricity supply if earthquake hits to minimize fires and explosions.
