PART 2 EARTHQUAKES

Question 1

3 methods of assessing earthquakes

Answer 1

1. long-term forecasting
2. short-term prediction
3. other methods

Question 2

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

Answer 2

Long-term forecasting

Question 3

T or F: In seismically active areas, small earthquakes are more likely to occur as the amount of time increases since the last major event.

Answer 3

False, LARGE earthquakes are more likely to occur as the amount of time increases since the last major event

Question 4

two important aspects in long-term forecasting

Answer 4

1. paleoseismology
2. seismic gaps

Question 5

study of prehistoric earthquakes

Answer 5

paleoseismology

Question 6

what does paleoseismology involve

Answer 6

seismologists will study sections of fault zones, particularly across/perpendicular to fault zone (offsets)

the study of offsets in sedimentary layers near fault zones to determine recurrence intervals of major earthquakes prior to historical records

they look into materials that can be dated: carbon, coal seams, peat lenses/layers

Question 7

a zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks.

Answer 7

seismic gap

Question 8

what happens if a seismic gap can be identified?

Answer 8

then it might be an area expected to have a large earthquake in the near future

Question 9

examples of areas with seismic gaps

Answer 9

1. Alaskan subduction zone
2. Acapulco Trench in Mexico (guerrero gap)
3. San Francisco and Parkfield Seismic Gaps along San Andreas Fault

Question 10

involves monitoring of processes that occur in the vicinity of earthquake prone faults for activity that signify a coming earthquake.

Answer 10

short-term prediction

Question 11

are predictions usually successful?

Answer 11

much of them fail

Question 12

Anomalous events or processes that may precede an earthquake are called ?

Answer 12

precursor events

Question 13

what do precursor earthquakes signal?

Answer 13

a coming earthquake

Question 14

why has short-term earthquake prediction been difficult to successfully obtain

Answer 14

• the processes that cause earthquakes occur deep beneath the surface and are difficult to monitor.
• earthquakes in different regions or along different faults all behave differently, thus no consistent patterns have so far been recognized

Question 15

what are the 6 earthquake precursors

Answer 15

1. increase in foreshocks
2. slight swelling/uplift or tilting of the ground surface
3. decreased electrical resistance
4. fluctuating water levels in wells
5. increased concentration of radon gas in groundwater
6. generation of radio signals

*also the behavior of animals

Question 16

example of how erratic behavior of animals preceded and earthquake

Answer 16

1976 Tangshan 7.4 Mag Tangshan Earthquake in China.
- snakes didn’t wanna go in their holes
- pandas were screaming
- fawns refused to go near water
*first systematic study, but could not recreate, succeeding studies were unsuccessful

Question 17

Causes microcracks to form prior to complete rupture, or main shock.

Answer 17

increase in foreshocks

Question 18

microcracks increasing the rock volume

Answer 18

Slight swelling/uplift or tilting of the ground surface

Question 19

water entering new void spaces that is more conductive than surrounding minerals.

Answer 19

Decreased electrical resistance

Question 20

water entering new cracks causes water
levels to lower; levels rise when voids close again.

Answer 20

Fluctuating water levels in wells

Question 21

new cracks allowing the gas, a radioactive decay product of uranium, to escape from rocks and enter wells.

Answer 21

Increased concentration of radon gas in groundwater

Question 22

caused by changes in rock strain or movement of saline groundwater.

Answer 22

Generation of radio signals

Question 23

6 differences between conventional and non conventional geophysical survey

Answer 23

intrusive, sensors, source, cost, scope, time
ISSCST

Question 24

3 examples of non-conventional/non-intrusive methods

Answer 24

1. microtremor survey method
2. refraction microtremor survey
3. horizontal-to-vertical spectral ratio method

Question 25

This method uses seven (7) portable seismometers that will record microtremors for a few minutes

Answer 25

microtremor survey method

Question 26

what are each instrument for microtremor survey method equipped with?

Answer 26

GPS for time synchronization and
location coordinates

Question 27

full GPS

Answer 27

Global Positioning System

Question 28

describe how refraction microtremor method works

Answer 28

1. A series of geophones planted on the ground connected to a seismograph
2. A hammer striking a steel plate is used as the seismic source
3. Propagating waves are measured and analyzed

Question 29

Uses the same instrument as the ones used in microtremor array method

Answer 29

horizontal-to-vertical spectral ratio method

Question 30

do you need to set up horizontal-to-vertical spectral ratio method as an array?

Answer 30

no, only single station

Question 31

describe the recording of horizontal-to-vertical spectral ratio method

Answer 31

Records fundamental ground period of an area

Only requires a recording time of 20 minutes at most

Question 32

4 ways to reduce earthquake risks

Answer 32

1. seismic engineering
2. early warning systems
3. planning and education
4. earthquake control?

Question 33

5+1 specific example of seismic engineering

Answer 33

Addition of cross-bracing and shear walls, base isolation, wrapping of columns with a steel jacket, and spiral wrapping technique on vertical reinforcing rods

dampers

Question 34

benefits of seismic engineering

Answer 34

➮provide greater structural strength with respect to the shear forces generated by lateral ground motion and a structure’s own inertia; and
➮reduce the actual amount of shear force that can develop on the structure.

Question 35

instead of demolishing old buildings with outdated designs or without any seismic controls, what can be done? examples?

Answer 35

A somewhat expensive, but viable option is to retrofit existing buildings with seismic controls

ie. exoskeleton outside building, weights on roof as pendulum to accommodate lateral movement

Question 36

The basic idea behind this is to take advantage of this time lag and the fact that P-waves do very little damage. The first P-wave then is simply used as an alert that the highly destructive S-waves and surface waves will soon follow.

Answer 36

Early Warning Systems

Question 37

3 specific examples of early warning systems

Answer 37

1. Only seconds are needed for preprogrammed systems to close valves on gas lines, thereby reducing the risk of uncontrolled fires.
2. Trains can be programmed to automatically stop.
3. Electric utilities can also shut down critical control systems on electrical grids and at power plants.

Question 38

the first step in planning and education as a way to reduce earthquake risks

Answer 38

➮The first step is to determine the level of severity of risk in a given area
➮by conducting hazard assessment
➮and subsequent construction of hazard maps.

Question 39

based on hazard assessments, what do government agencies do to mitigate earthquake hazards?

Answer 39

➮government agencies will develop building codes
➮that require appropriate levels of seismic engineering in buildings and other structures

Question 40

in terms of education what can be done to reduce earthquake risk?

Answer 40

➮Raising of awareness on what to do before, during, and after an earthquake on all levels of society, from school-aged children up to emergency management
officials.
➮Regular earthquake drills

Question 41

examples of how humans can induce earthquakes

Answer 41

1. fluids can change affect the energy distribution of rocks (dam construction, injecting toxic wastes into wells, injection of water in fault zones)
2. nuclear testing (explosions causing earthquakes) and blasting in mine sites