Earthquakes - METHODS OF ASSESSING EARTHQUAKES Flashcards
(51 cards)
three methods of assessing earthquakes
long-term forecasting
short-term prediction
other methods (gephysical)
based mainly on the knowledge of when and where earthquakes have occurred in the past
long-term forecasting
long term forecasting are based on ______ and _____
historical records and geologic evidences
t or f: in seismically active areas, large earthquakes are more likely to occur as the amount of time increases since the last major event
T
two important aspects of long-term forecasting
paleoseismology
seismic gaps
study of prehistoric earthquakes
paleoseismology
what is paleoseismology
study of prehistoric earthquakes by studying offsets in sedimentary layers near fault zones and looking into materials that can be dated
materials that can be dated in paleoseismology
coal seams, peat
paleoseismology determines
recurrence intervals of major earthquakes prior to historical records
paleoseismology is done thru:
trenching
depth of trenching:
width of trenching:
2m;
depends on the fault
formation of sand blows is linked to
liquefaction
sand and water that come out onto the ground surface during an earthquake as a result of liquefaction
sand blows
what type of dating are used in sand blows to determine earthquake event?
radiocarbon dating
a zone along a tectonically active area where no earthquakes have occurred recently but is said to be still accumulating strain
seismic gaps
it was known as a gap before the september 15, 1985 earthquake
Former Michoacan Gap
two gaps along the cocos plate and acapuclo trench
Former Michoacan Gap and Guerrero gap
involves monitoring of processes that occur in the vicinity of earthquake prone faults that may signify a coming earthquake
short-term prediction
anomalous events or processes that may precede an earthquake
precursor events
successful short term prediction have been difficult to obtain because:
earthquakes are generated deep beneath the surface and are difficult to monitor
t or f: no consistent patterns for short-term prediction have been recognized because earthquakes in different region or faults all behave differently
T
earthquakes precursors
- increased foreshocks
- slight swelling/uplift or tilting of ground surface
- decreases electrical resistance
- fluctuating water level in wells
- increased radon concentration in groundwater
- generation of radio signals
these form prior to complete rupture
microcracks
t or f: microcracks decrease the volume of rocks
F (increase)
