earthquakes

Question 1

define earthquakes

Answer 1

sudden shaking or vibration of earth’s crust due to the movement of tectonic plates
the plates do not move smoothly and can become stuck due to friction which causes a slow build up of energy or pressure along the plate boundaries
if this energy is suddenly released via seismic waves a violent jerking movement occurs on the surface
occur at all types of plate boundary movements

Question 2

define focus/hypocentre

Answer 2

point below earth’s surface where energy is released or earthquake originates

Question 3

epicentre

Answer 3

point on the surface of earth above the focus where most shaking is felt and where most severe damage caused will occur

Question 4

seismic waves

Answer 4

shockwaves radiate out from focus responsible for shaking felt on the ground and felt most strongly at the epicentre becoming weaker as travel further away

Question 5

fault

Answer 5

line or crack where movement occurs triggering the earthquake

Question 6

intensity

Answer 6

describes level of shaking during an earthquake

Question 7

magnitude

Answer 7

energy released by earthquake

Question 8

how are earthquakes measured

Answer 8

measured on 10 point Richter scale – logarithmic scale with each increase in magnitude of the earthquake the amount of ground shaking increases by 10 times and amount of energy released increases 32 times

Question 9

seismograph

Answer 9

device which detects and records earthquakes

Question 10

what do vibrations due to seismic waves cause

Answer 10

both lateral and vertical movement

Question 11

define foreshocks

Answer 11

small temors that precede earthquake

Question 12

define aftershocks

Answer 12

small tremors that follow earthquake which can continue for several weeks afterwards

Question 13

how long does the main earthquake last

Answer 13

less than a minute

Question 14

define tremors

Answer 14

seismic waves released by earthquakes can lead to ground shaking or tremors
most intense closest to epicentre
decrease with increasing distance from epicentre
can lead to collapse of buildings or bridges
may also trigger landslides on unstable slopes – 1994 6.7 magnitude earthquake triggered over 11 000 landslides in the San Fernando Region
if cause gas pipes to burst and fires to occur
earthquakes in Czech republic and germany

Question 15

define ground fissures

Answer 15

during an earthquake shaking on ground may result in long narrow cracks on surface of earth

Question 16

explain soil liquefaction

Answer 16

happens when vibrations from earthquakes causes sediment to behave like quicksand during an earthquake
the shaking causes an increase in water pressure which results in loosely packed water saturated soil to behave like a liquid and thus causes buildings to lean and collapse
tends to occur where there is water saturated or unconsolidated soil to reclaim land
mexico city earthquake 1985
magnitude of 8.1 or richter scale
built on old lake bed more than 10 000 dead
30 000 injured
more than 400 buildings collapsed and thousands more damaged leaving over
250 000 homeless
port royal earthquake of jamaica

Question 17

list factors which contribute to damage

Answer 17

time of day
climate
aid - how quickly emergency responds
magnitude – san francisco 1906 claimed 700 lives although taiwan 1999 was of smaller magnitude claimed 2300
location of epicentre and focus - closer to epicentre the greater the amount of damage — november 2007 7.4 magnitude martinique however damage was minimal since focus was very deep below at dpeth of 143 km
if area affected is densely populated and highly built up
close proximity of buildings and leaking gas and power mains cause fires to break out and spread easily
of tsunamis accompany earthquakes 2004 indian ocean earthquake took lives of almost 280 000 and inundated coastal communities across south and southeast asia
boxing day sumatra indonesia 9.1 to 9.3 caused entire planet to vibrate and caused earthquakes in alaska waves up to 30 m in height to the east coast of africa

Question 18

how to reduce impact

Answer 18

forecasting with rapid appearance and growth of irregular bulges on surface and changes in water levels to the ground
evacuating people from cities
1975 haicheng china 90 000 evacuated before earthquake of 7.3
strengthened with steel pillars which are flexible enough to sway to accommodate ground movements caused by earthquake
fireproof materials used
construction of roads transport routes and passageways should facilitate evacuation rescue operations and transport of relief supplies to people in earthquake zone
drills and public education to increase preparedness and awareness among citizens
sufficient relief supplies shelters and medicines prepared