9 - Assessing and mitigating earthquake hazard Flashcards
what is probabilistic seismic hazard assessment
the probability that a given location will experience shaking leading to sone value of seismic intensity or ground acceleration, over a defined time interval into the future
how are earthquakes monitored
- seismometers
- strong motion accelerometers
- tilt and strain meters
- Geodetic surveys inc. GPS
- satellite radar inferometry
- sea floor hydrophone arrays
- ocean floor pressure gauge
what are some precursors of earthquakes
- decrease in seismic velocity
- ground deformation
- geomagnetic field variations
- geo-electromagnetic variations
- foreshocks
- slow slip events
- ground water flow or level change
- radon gas emission
- animal behaviour
what happens with increasing fluid pressure
can trigger earthquakes - pore fluid in brittle crust can reduce strength if rock
how is earthquake potential assessed
- instrumented records
- historic record
- paleoseismology
- geological analysis of faults and plate motions
what is ground acceleration
a measure of the movement of ground during an earthquake in g or m/s2
what is hazard
the probability of ground shaking of a particular intensity or acceleration and/or secondary hazards
what is vulnerability
degree of loss of life, injury and damaged likely to be sustained by a specific structure, area or community if exposed to ground shaking
what is risk
- Risk = Hazard x Vulnerability
- a function of the hazard and vulnerability of the region and population
- probability of damage to people and buildings
what is mitigation
steps to reduce the risk and vulnerability. related to engineering, population preparedness and behaviour
how do ground conditions effect seismic waves
seismic waves are amplified in soft, low density sediments relative to rock e.g. coasts and reclaimed land
what are good building materials in earthquake zones
strong and flexible materials e.g. steel and timber
