Geohazards

Question 1

geohazard def

Answer 1

a geological condition that is dangerous/ potentially to enviro or people who live within it

Question 2

examples of geohazards

Answer 2

earthquakes
vol eruptions
tsunamis
landslides
subsidence
avalanche
cliff fall

Question 3

what is the focus and epicentre of an earthquake

Answer 3

focus-where movement occurred

point within the earth at which the earthquake og as movement occurs along fault plane

sesmic waves radiate away from it in all directions

epicentre point on surface above focus

Question 4

how is stored elastic strain energy released?

Answer 4

stress = forces
strain = reaction

relative movement of rock on either side of fault applies stress

rock undergoes strain

this process transfers energy and increases elastic strain stored in rock

energy releases and elastic energy decreases

energy released due to movement

released as heat and seismic waves (greater amp greater energy)

Question 5

amplitude def

Answer 5

maximum extent of displacement of an oscillation from the position of rest

Question 6

what does amplitude show

Answer 6

greater the amp = greater energy released

Question 7

what happens to amp as waves move away from focus

Answer 7

reduces as energy released and transferred to surrounding rock

Question 8

attenuation of seismic waves

Answer 8

loss of energy experienced by a wave shown as reduction in amp as it propagates through material

waves faster through rigid as transfer is easier so attenuation is reduced in more rigid rocks

amp decreases with distance from focus

Question 9

Mercalli scale

Answer 9

magnitude scale for measuring earthquakes

empirical

gives 12 categories earthquake can fall into based on destruction and how people felt it
instrumental to cataclysmic

Question 10

Mercalli scale pros and cons

Answer 10

pros-
don’t need specific equation
don’t need formal training to understand

cons-
empirical (based on observation/experience )

subjective

not comparable - e.g. all observation relate to building but they are diff in each country

may not remember experience

intensity decreases from focus but mag doesn’t

Question 11

different earthquake measurement systems in time order

earliest to oldest

Answer 11

Mercalli- Richter- moment mag

Question 12

Richter scale

Answer 12

measures energy output of the earthquake

1-10

use seismogram:
lag time - time diff between P and S waves tells us distance from focus
height of greatest S wave

plot on richter scale graph tells mag

should give same value no matter where

log so 1= 10x amp

Question 13

Pros and cons of Richter scale

Answer 13

Pros:
Maths equ so less subjective
but also has desc for public

Cons:
assume same rock type

larger is underrepresented and less accurate the larger it gets (seismologists only measured at certain frequencies)

outdated

Question 14

moment magnitude scale

Answer 14

What is used now

when waves arrive at seismometer measure:
lag time - tells us distance from focus
amplitude and waves
actual displacement of rock at quake site (new, not in richter)

Question 15

Pros of moment mag

Answer 15

interpret broader range of seismic frequencies- determines more accurate e from large earthquake

accounts for rock type and rigidity

Question 16

moment mag equ
(given to us)

Answer 16

Mw= 2/3logE-6.1

Question 17

different wave types

Answer 17

P- primary
S- secondary
L-love
R-rayleigh

Question 18

features of P waves and effect on buildings

SEE BOOKLET FOR DIAGRAM

Answer 18

features-
travel through L and S

body waves

arrive first- fastest

longitudinal

effect on building-
least dangerous

Question 19

features of S waves and effect on buildings

SEE BOOKLET FOR DIAGRAM

Answer 19

features-
can travel through S

body waves

arrive second- second fastest

shear waves - transverse

effect on buildings-
S waves more destructive than P
as greater amp

horizontal worse than vertical

Question 20

features of L waves and effect on buildings

SEE BOOKLET FOR DIAGRAM

Answer 20

Features-
Surface waves do the most damage

shear wave where shearing motion is confined to horizontal plane at earths surface (oscillate)

effect on buildings-
responsible for most damage

greatest effect- sideways movement is more effective

Question 21

features of R waves and effect on buildings

SEE BOOKLET FOR DIAGRAM

Answer 21

features- surface waves are most destructive

slowest

earths surface moves in a vertical elliptical path parallel to wave movement

effect on building-
worse than P and S

most movement with R- up and down so less destructive

Question 22

effect on ground movement on built environment

Answer 22

L waves cause most damage to buildings

lose objects thrown upwards

buildings fracture
pancake

freeways collapse

brick and stonework seperate along motar

sects of utility pipes separate

Question 23

how does rock competency affect how e is transferred and effect on buildings

Answer 23

comp rocks allow easier propergation of seismic waves and move on

less e dissipated to rock

less movement

also moves quicker through comp rock

Question 24

liquefaction and effect on buildings

Answer 24

saturated or partially saturated unconsolidated material losing strength and rigidity in response to applied stress

e.g. Earthquake

unconsolidated and incompetent rock holds more H2O in pore spaces

when rock compressed due to seismic waves, pore spaces reduce and H2O comes up and out

loss of strength makes buildings tip and sink

Question 25

where are developments banned

Answer 25

soft unconsol rock or incomp

on fault zone

nearby fault zones

Question 26

earthquake engineering ideas

Answer 26

reenforce concrete with steel

base isolation

tuned mass damper- giant pendulum near top of building brings back to centre by swing in opp direction (Taipei 101)

Crossbracing- X shaped brackets transfer seismic forces back to ground reducing lateral movement

seismic damper- absorb energy

emergency shut off switch

rubber/flexi pipes

metal plates around building- easier to move through than building as more rigid reduces impact on building)