Chapter 10- Geohazards

Question 1

amplitude

Answer 1

maximum extent of an oscillation. measured from position of rest

Question 2

attenuation

Answer 2

loss of energy experienced by a wave, shown by reduction of amplitude as it propagates through a material

Question 3

moment

Answer 3

turning effect of a force around a pivot

Question 4

relationship to define magnitude

Answer 4

M (magnitude) is directly proportional to 2/3 log E (energy)
M = 2/3 log E -Q
Q is taken to be 6.0

M = 2/3 log E - 6.0

Question 5

liquefaction

Answer 5

(partially) saturated, unconsolidated material losing strength and rigidity in response to applied stress- usually an earthquake

Question 6

resonant frequency

Answer 6

the frequency at which the amplitude of the oscillation us greatest

Question 7

intensity

Answer 7

measure of the surface shaking and damage of an earthquake

Question 8

effects of liquefaction on the built environment

Answer 8

-flow failures
-lateral spreads
-ground oscillation
-loss of bearing strength

Question 9

frequency

Answer 9

no. oscillations per second or no. waves passing by a fixed point per second. measured in hertz

Question 10

resonance

Answer 10

tendency to oscillate with greater amplitude at certain frequencies

Question 11

civil engineering for areas with earthquakes

Answer 11

-planning and risk assessment
-building design: height, regular, symmetrical design, avoid ornamentation, flexible, reinforced foundations
-ground/base isolation systems
-resisting sheer forces, ie avoiding pancaking
-absorbing sway, active mass dampeners or controlled rocking frame system
-flexible piping for services

Question 12

natural frequency

Answer 12

f (frequency) = 1/2 pi x (sqr k (stiffness) / m (mass))

Question 13

geological hazard

Answer 13

geological condition that is (potentially) dangerous to the environment and people living within it

Question 14

seismic risk

Answer 14

possibility of suffering harm or social/environmental loss due to a seismic event

Question 15

probability

Answer 15

likelihood an event will occur. quantified between 0 and 1

Question 16

return period

Answer 16

average length of time for an earthquake of a given magnitude to occur again or be exceeded
T = (n (number of years on record) + 1) /m (number of recorded earthquakes)

Question 17

forecast

Answer 17

statement of the probable occurrence of an event calculated from data

Question 18

prediction

Answer 18

a statement about what you think will happen in the future

Question 19

determinism

Answer 19

finding outcomes through known relationships- cause and effect

Question 20

warnings for an earthquake (not proven completely successful)

Answer 20

-physical properties- sometimes larger earthquakes are preceded by smaller earthquakes
-coloured lights in the sky may be caused by changes in electrical properties of quartz/other minerals under stress
-cracks developing in rocks under stress
-tilting of the area around the focus
-lowering of water table
-animal behaviour, potentially can sense the amplitude before us or can detect changes in the magnetic field
- radon emmissions
-seismic gap model

Question 21

tsunami hazard management

Answer 21

-efficient warning system
-obviously placed signs showing evacuation routes
-public education campaigns
-reducing energy of the waves by maintaining coral reefs, coastal trees and vegetation

Question 22

plasticity

Answer 22

the property a substance has when deformed continuously under a finite force

Question 23

kaolin-serpentine clay

Answer 23

1:1
kaolinite, serpentine
non expanding, low shrink swell

Question 24

smectite clay

Answer 24

2:1
montmorillonite, saponite
expanding, high shrink swell

Question 25

vermiculite

Answer 25

2:1 vermiculite limited expansion, medium shrink swell

Question 26

mica

Answer 26

2:1 illite, muscovite, biotite non expanding, low shrink swell

Question 27

tilt

Answer 27

calculated as the change in elevation between two points divided by the distance between them maximum tilt occurs at the point of inflection in the subsidence trough usually expressed as millimeters per meter

Question 28

inflection point

Answer 28

a point on a curve at which it changes from being convex to concave

Question 29

sinkholes

Answer 29

hollows or holes in the ground caused by collapse of a surface layer, usually by dissolution of limestone

Question 30

talus

Answer 30

the debris accumulating at the foot of a slope due to erosion of the rock face above

Question 31

translation slide

Answer 31

when material begins to move as an entity eg several beds sliding down slope. typically breaks up as it gathers speed and energy increases

Question 32

isotropic clay

Answer 32

having equal properties in all directions. not the same as homogeneous - conveys being made of the same material throughout - a slate can be homogeneous, made of metamorphosed mudstone but not isotropic as it has cleavage

Question 33

tsunamite

Answer 33

a tsunami deposit sedimentary unit deposited during the inudation phase offshore deposits as water retreats are different

Question 34

types of mass movement, slow to fast

Answer 34

creep, slumps, slides, flows, falls

Question 35

triggers for mass movement

Answer 35

-human actions such as building on slopes or clear felling them -heavy rainfall -sudden falls in the water table -earthquakes

Question 36

methods of slope stabilisation

Answer 36

-reducing the angle of the slope/slope modification -retaining wall -gabions -rock bolts -rockdrains -wire netting -shotcrete -vegetation

Question 37

fabric

Answer 37

describes the spatial and geometric configuration of all the components of a rock- mineral and crystal size, shapes and relative orientation, voids etc. close to term 'texture' used for igneous and metamorphic

Question 38

confining pressure

Answer 38

combined lithostatic and hydrostatic pressure. At depth all principle stresses are equal

Question 39

ductile deformation

Answer 39

occurs when a rock suffers large strains without large-scale fracturing. it bends and flows

Question 40

brittle deformation

Answer 40

causes the rock to fracture, possible after some elastic deformation has occurred

Question 41

principle stresses

Answer 41

a useful way to describe what is going on. o1 is the maximum, o3 the minimum and o2 the intermediate principle stress direction. all three are perpendicular to each other

Question 42

lithostatic pressure

Answer 42

vertical pressure due to the mass of the rock only. also known as the overburden pressure

Question 43

Uniaxial Compressive Strength Test

Answer 43

-measures rock strength -cylinders of rock placed in a hydraulic press. -load is increased slowly (one micrometer per second), and recorded until the sample fails at peak strength -'unaxial' bc principle stress is down the axis of the cylinder, other stresses are negligible

Question 44

asperity

Answer 44

describes the roughness of the surface of a discontinuity

Question 45

residual strength

Answer 45

remaining resistance to movement after the rock has failed and been displaced

Question 46

joint sets

Answer 46

fractures across which there is little displacement. mostly to dissipate the residual stresses left after folding. result of regional stresses so tend to form sub parallel sets

Question 47

formula for hydrostatic pressure

Answer 47

P = pgh Fluid pressure = fluid density x acceleration due to gravity x fluid depth

Question 48

geotechnical site investigations

Answer 48

-desk study -site surface mapping -geophysical surveys -site subsurface mapping - rock and soil property measurements -geohazard mapping -integration of data

Question 49

drift

Answer 49

superficial deposits such as glacial and fluvioglacial material. 'solid' maps show an overlay of drift. alluvium refers to recent deposits by rivers

Question 50

seismic refraction surveys

Answer 50

can be made using a simple dropped mass or large hammer as an energy source. waves are refracted by changes in velocity such as at the base of the weathered layer