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Geohazard > Earthquakes - METHODS OF ASSESSING EARTHQUAKES > Flashcards

Earthquakes - METHODS OF ASSESSING EARTHQUAKES Flashcards

1
Q

three methods of assessing earthquakes

A

long-term forecasting
short-term prediction
other methods (gephysical)

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2
Q

based mainly on the knowledge of when and where earthquakes have occurred in the past

A

long-term forecasting

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3
Q

long term forecasting are based on ______ and _____

A

historical records and geologic evidences

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4
Q

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

A

T

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5
Q

two important aspects of long-term forecasting

A

paleoseismology
seismic gaps

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6
Q

study of prehistoric earthquakes

A

paleoseismology

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7
Q

what is paleoseismology

A

study of prehistoric earthquakes by studying offsets in sedimentary layers near fault zones and looking into materials that can be dated

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8
Q

materials that can be dated in paleoseismology

A

coal seams, peat

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9
Q

paleoseismology determines

A

recurrence intervals of major earthquakes prior to historical records

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10
Q

paleoseismology is done thru:

A

trenching

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11
Q

depth of trenching:
width of trenching:

A

2m;
depends on the fault

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12
Q

formation of sand blows is linked to

A

liquefaction

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13
Q

sand and water that come out onto the ground surface during an earthquake as a result of liquefaction

A

sand blows

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14
Q

what type of dating are used in sand blows to determine earthquake event?

A

radiocarbon dating

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15
Q

a zone along a tectonically active area where no earthquakes have occurred recently but is said to be still accumulating strain

A

seismic gaps

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16
Q

it was known as a gap before the september 15, 1985 earthquake

A

Former Michoacan Gap

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17
Q

two gaps along the cocos plate and acapuclo trench

A

Former Michoacan Gap and Guerrero gap

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18
Q

involves monitoring of processes that occur in the vicinity of earthquake prone faults that may signify a coming earthquake

A

short-term prediction

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19
Q

anomalous events or processes that may precede an earthquake

A

precursor events

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20
Q

successful short term prediction have been difficult to obtain because:

A

earthquakes are generated deep beneath the surface and are difficult to monitor

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21
Q

t or f: no consistent patterns for short-term prediction have been recognized because earthquakes in different region or faults all behave differently

A

T

22
Q

earthquakes precursors

A
  1. increased foreshocks
  2. slight swelling/uplift or tilting of ground surface
  3. decreases electrical resistance
  4. fluctuating water level in wells
  5. increased radon concentration in groundwater
  6. generation of radio signals
23
Q

these form prior to complete rupture

A

microcracks

24
Q

t or f: microcracks decrease the volume of rocks

A

F (increase)

25
Q

water entering void spaces results in a _____ in electrical resistance

A

decrease

26
Q

water entering new cracks causes water in well to ______; and will ______ when voids are closed again

A

lower ; rise again

27
Q

t or f: radon is an inert gas, meaning it is non-reactive

A

T

28
Q

radon is a radioactive decay product of ____

A

uranium

29
Q

radon escape from ____ and enter ____-

A

rocks ; wells

30
Q

radio signals are caused by

A

changes in rock strain;
movement of saline groundwater

31
Q

advantages of non-conventional / alternative geophysical surveys

A

non-intrusive;
sensors are planted on the ground;
utilizes passive sources;
cost-effective
cover wide area and up to 3km deep
fast and efficient, 4 hrs max

32
Q

examples of passive sources

A

ambient noise, microtremors

33
Q

three types of non-conventional methods

A

microtremor survey method
refraction microtremor survey
horizontal-to-vertical spectral ratio method

34
Q

microtremor survey method uses

A

7 portable seismometers

35
Q

each instrument in microtremor survey method is equipped with ______ for _____ and _______

A

Global Positioning System ;
time synchronization and location coordinates

36
Q

microtremor surveys records

A

microtremors for a few minutes

37
Q

a hammer striking a steel plate is used as a seismic source

A

refraction microtremor survey

38
Q

in refraction microtremor survey, a series of _____ are planted on the ground and connected to _______

A

geophones ; seismograph

39
Q

in refraction microtremor surveys, ________ were measured and analyzed

A

propagating waves

40
Q

uses the same instrument as microtremor survey method but only a single station

A

horizontal-to-vertical spectral ratio method

41
Q

what does horizontal-to-vertical spectral ratio method record?

A

ground period of an area

42
Q

recording time required for horizontal-to-vertical spectral ratio method

A

20 mins at most

43
Q

reducing earthquakes risk (4)

A
  1. structural engineering
  2. early warning systems
  3. planning and education
  4. earthquake control?
44
Q

seismic engineering provide greater structural strength with respect to the ____ generated by ______ and structure’s own ________

A

shear forces ; lateral ground motion ; inertia

45
Q

seismic engineering methods

A

shear walls
cross bracing
base isolation
steel jacket
steel jacket wrapped spirally

46
Q

a somewhat expensive but viable option to make existing buildings resistant to lateral movement is to _____

A

retrofit existing buildings with seismic controls

47
Q

the basic idea behind an early warning system is to take advantage of the ______ and the fact that

A

time lag ; P waves do very little damage

48
Q

the first ______ is simply used as an alert that a highly destructive _____ and ______ will follow soon

A

P-waves ; S waves ; surface waves

49
Q

examples of early warning systems

A

close valves on gas lines
shut down electrical powers
trains stopped

50
Q

planning and education for earthquake includes:

A

hazard assessment
development of building codes
informing people on what to do before, during and after
regular earthquake drills

51
Q

examples of human induced eartquakes

A
  1. hoover dam blocked colorado river generated 600 earthquakes , one with mag 5 and 2 with mag 4
  2. injection of toxic waste in disposal wells, generated earthquake 4-8 km below 3.8 km well
  3. underground nuclear testing generated 6.3 magnitude earthquake, aftershock was mag 5

Geohazard (25 decks)

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