Mid Term Natural Hazards and Disasters

For something to be a disaster

loss of life, economic loss

Natural Hazard

geological or natural phenomenon causing danger or risk to life, property or environment. A hazard is a threat

Natural Hazard

Hazardous event causing loss of life, hardship, and or economic loss/ damage

Disaster

result of hazard. occurs when hazard meets vulnerability

disaster risk formula

hazard x exposure x vulnerability

Exposure function of location

of the hazard, of people

resiliance

ability to persist

Disaster management cycle

Disaster, response, recovery, mitigation, preparedness

Response

Actions taken during and immediately after an event humanitarian aid, damage assessment

Recovery

rehabilitation and reconstruction efforts after the an event

Mitigation

Actions taken before an event to reduce its impact

Preparation

Emergenct planning, early warning systems, and capacity building

Global trend

Trending towards zero or negative

Future projection

Reach a maximum then begin to decline UN projection of 10.3 in the mid 2080’s

Population change

Addition ( birth rates) Subtractions ( death rate)

Natural population change

Number of births - number of deaths if the number is positive population growth.

Demographic Transition Model

population changes in response to economic development

Death rates drop

Greater access to clean water, medical care, etc.

Birth rates drop but with a lag

increased economic opportunities for women and reduced incentive for large families

Natural population growth

Birth rates are higher than death rates

Curved triangle High birth rate high death rates

population increase (slow)

Straight triangle High birth rate falling death rates

population increase rapid

Half oval falling to low birth rates falling death rates

slowing population stable population

round oval low and falling birth rate low death rate

declining population

Frequency

the number of events occurring during a specific time high frequency events occur often low frequency events occur rarely

Magnitude

physical size or energy released by event high events typically more powerful low events are less powerful

Geophysical category disaster

directly caused by internal earth processes and energy examples earthquakes, volcanic activity

Weather/climate category disaster

effects of external energy on earth’s atmosphere and hydrosphere severe weather, tropical cyclones, floods, droughts

Hybrid disaster category

may be internal or external energy process can be triggered by another hazard mass movement, tsunami

compositional layers of the earth

crust, mantle, core

Crust

uniform, thin primarily made of silicon and oxygen

Oceanic crust

Mafic relatively low silica content

Conitental crust

Complex varied and thicker felsic relatively high silica content oceanic and continental types low density

Mantle

Solid rock ultramafic very low silica content high density

Core

inner core solid outer core liquid mostly iron and nickel metallic no silica very high density

Pressure and temperature of internal earth

Both increase with depth in the earth

Internal earth energy heat

Primordial, radioactivity

Primordial heat

generated during planet formation

Radiactivity

decay of unstable atoms in earth’s materials

internal energy

drives processes like plate tectonics leading to earthquakes, volcanoes, and other related phenomena

Earths external energy sources

sun, surface processes

Sun

solar radiation drives atmospheric and oceanic circulation including the hydrologic cycle surface processes (the weather)

Mechanical behavior

How materials respond to stress Brittle, ductile

brittle

breaks under stress

Ductile

deforms without breaking

Earths mechanical layers

Lithosphere, Asthenosphere

Lithosphere

rigid, brittle solid, crust and mantle

Asthenioshere

ductile solid “soft plastic” located upper mantle

effects of the plastic asthenopshere

Flow can flow, vertical movement and horizontal movement of lithosphere , heat transfer allows by convection

Plate movement

earths brittle later (lithosphere) is broken into large fragments called plates these plates move horizontally on top of the plastic asthenosphere

Faults

plate boundaries are fracrtures called faults

how are earthquakes caused

movement of rocks along faults most earthquakes occurs on faults. the most dangerous earthquakes are associated with plate boundaries. volcanos and mountains are often aligned with plate boundaries

types of plate boundaries

types of plate boundary between two plates is determined by there relative motion

types of plate boundaries

convergent, divergent, transform

convergent

moving toward each other, destructive (seafloor is destroyed/ recycled) rocks require significant stress to fail under pressure. Failure produces giant earthquakes

Divergent boundaries

Moving away from each other, constructive (new seafloor is created), rocks under pressure fail relatively easy generally small earthquakes typically at sea.

Transform boundaries

sliding past each other, conservative (no material is created or destroyed), moderate stress is required for rocks to slide along a fracture. Moderate to large earthquakes.

Convergent boundaries

Ocean-Ocean, Ocean Continent, Continent- Continent

Ocean- Ocean Subduction Zone

Shallow to deep earthquakes, oceanic trenches volcanic island chains. Subduction process one tectonic plate moves under another and sinks ( destructive)

Ocean- Continent

Subduction Zone, mountains, chain of volcanos, oceanic trenches. shallow earthquakes at or near boundary. earthquakes get progressively deeper away from boundary in direction of Subduction

Continent-continent

no subduction continental crust to buoyant , crust thickening, mountains shallow mainly earthquakes

Divergent boundaries

Shallow earthquakes, volcanismm topographic ridges, sea floor spreading

Sea floor spreading

occurs when 2 tectonic plates move away from each other creating new crust (constructive process)

Transform boundaries

can be continental or oceanic, mid ocean ridges (divergent segments) are linked by transform faults.

Driving force of plate movement

Driven by earths internal heat

Driving forces of plate movement

Primary energy, convetion, gravity, slab pull, ridge push

Primary heat source

earth’s internal energy (heat)

Convection

Hot core causes the overlying mantle to convert transferring heat and driving plate motion

Gravity

plays a role through slab pull and ridge push

Slab pull

denser older plates at subduction zones sink due to gravity

Ridge push

younger warmer buoyant plates at ridges are pushed up and out

Seismic wave

energy released from a rock movement (usually a fault)

Causes of earthquakes

Plate tectonics- earths lithosphere responds to stress by fracturing when rocks on other side of fracture move relative to each other it creates a fault.

Left lateral strike slip fault

relative to one side the other side of the fault moves left

right lateral strike slip fault

relative to one side the other side of fault moves right

Normal fault

one side moving down

reverse fault

one side moving up

thrust fault

fault dips shallowly

Elastic rebound theory

1) applied stress: stress (force per unit area) acts on a fault

2) elastic strain: When the stored energy becomes to much for the rocks to handle the fault breaks suddenly

3) rebound: the rocks snap back to a less strained position, releasing energy in the form of seismic waves (earthquakes.

Earthquake terminology

Fault Scarp: surface expression of fault

Socus/ hypocenter: point where rupture first begins

epicenter: point on surface directly above hypocenter

P wave

direction of propagation: ——> particle motion ←—→

S wave

direction of propogation ——→ particle motion up/down

love surface wave

direction of propagation ——> particle motion ^l v

raleigh surface wave

direction of propagation —→ particle motion in a circle <)

Seismic wave velocities

p wave > s wave > surface waves

determining distance to earthquake

time interval between arrival of p wave and the s wave S-P interval increases with increasing distance from earthquake

Earthquake magnitude

represents the relative size or energy realized by an earthquake

richter magnitude

most common used scale in media and is relatively easy to determine but less reliable each whole number is a: 10x increase in seismogram amplitude and 32x increase in energy release.

Richter magnitude can be determined using an earthquake seismogram

key factors: 1) amplitude (height) of the largest S-wave 2) distance to the epicenter (from the seismometer [based on s-p interval])

Moment magnitude

prefered for scientific research based on physical parameters of the Sault and sesmic movement. calculated by strength of rocks x rupture of fault x average slip on faults. more accurate difficult to calculate

Intensity

How strong shaking felt and damaged caused measured by mmi scale. things that affect intensity how big, har far away, how deep, how long it shook

earthquakes don’t kill people building do

direct effects ground shaking, material amplification, liquefaction (how soil behaves. indirect effects: surface rupture, uplift, design and construction. Secondary disasters tsunamis, lanslides, fires, vertical displacment of water

Material Amplification of shaking

Softer rock amplifies seismic waves more that hard rock leading to increased shaking

Construction practices and resonance

Resonance: Occurs when a structures natural vibration frequency matches the seismic wave frequency leading to extreme shaking matches building natural wobble

Flawed building designs

Structures with wings additions or different heights, different properties too close together, soft first stories ( parking garages) that cant support upper floors, non continuous steel bars/ columns

Mitigation Strategies

For existing buildings, changing building height, move weight to lower floors, change building shape, change material, change base attachment. for new structures implement strong building codes.

Volcanos

molten rock and gases escape to the surface of planetary- mass objects

Volcanic subduction zones

occurs convergent plate boundaries 10% of volcanic activity grey volcanos (ashy)

Hot Spots

locations where anomalously hot mantle material rises to the surface leading to volcanism. 10% of volcanic activity. may or not be related to plate boundaries. red lava volcanos/ eruptions

Spreading centers

found at mid ocean ridges and divergent boundaries. responsible for about 80% of volcanic activity. Associated with the formation of new sea floor red lava volcanos/ eruptions