LANDSLIDES AND EARTHQUAKES

TYPES OF MATERIALS IN LANDSLIDES

ROCK:

SOIL/EARTH: rock exposed to the atmosphere plus microbiological and organism activity

MUD: mixture of mainly water

DEBRIS: a mixture of the above.

TYPE OF MOVEMENT IN LANDSLIDES

FALLS: think of the end of a cliff breaking off, not in contact with anything whilst it moves. Occurs on very steep slopes (usually rock) as Material detaches because of weakness (fractures etc.) it Falls due to gravity and is Very fast!

SLIDES: Vary from slow to fast. Usually soil, rock or debris Material moves as a coherent mass along a surface of failure (either curved or straight) Curved/bowl shaped failure surface: Rotational slide (slump)

FLOWS: fluid motion (Chaotic, can be fast or slow)

- Very slow to very fast (mudflows up to 80 km/h!)

- Soil, mud, wet debris, (rock)

- Water is usually very important

- Fluid or plastic flow of material (chaotic

COMPLEX MOVEMENTS:

-Combinations of Mass movements

-Eg. A slide that becomes a fall

-Eg. A slide that becomes a flow

TYPES OF SLIDES IN LANDSLIDES

1. ROTATIONAL (Slump). If surface is curved

- Intermediate Speed

- Usually weak material (sediment)

- Rotation of material on a curved failure plane

- Often characterized by a curved scarp above the slide

2. TRANSLATIONAL SLIDE

- Slow to fast

- Usually strong

material moving on

planes of weakness

- Cohesive motion of

material along a flat

surface SLABS OF ROCK MISSING

RATE OF MOVEMENT IN LANDSLIDES

If the movement is "slow" or slower the name will be:

Creep, Soil flow, or Earth flow

Soil Creep - Ireland

Speed of mm/yr - cm/yr

ANGLE OF REPOSE IN LANDSLIDES

Loose materials rest at a natural angle of repose, the STEEPEST ANGLE at which the material can accumulate without sliding. DEPENDS ON...

- The material (clay silt, sand, etc.)

- Particle size and shape

- Moisture level

FORCES INVOLVED WITH THE STABILITY OF SLOPES LANDSLIDES

1 DRIVING FORCE: GRAVITY AND SHEAR STRESS: looks like a fancy t <- but uppercase.

2 SHEAR STRESS: Shearing is motion from side to side

• Component of the force of gravity parallel to the slope

3 GRAVITY POINTS DOWN. sheer stress: how gravity is manifesting itself.

4 SHEER STRESS: what brings gravity DOWN THE SLOPE.it is parallel to the angle of the slope. EG: 90 degree is big sheer strength cause that boy wanna bring you down

5 SHEER STRENGTH: resistance to bringing gravity down the slope. eqb type shit

RESISTING FORCES IN LANDSLIDES

prevent slopes from failing (shear strength as well as frictional and cohesive strength)

FRICTIONAL STRENGTH IN LANDSLIDES

Resistance to sliding (proportional to normal force/stress) eg: compare sand being piled up to rocks. angle is different

COHESIVE STRENGTH IN LANDSLIDES

How the material holds together

FACTOR OF SAFETY IN LANDSLIDES

Fs = Tf (sheer strenght) / T (sheer stress) Fs >> 1.0 stable slope ||||| Fs < 1.0 Fail!

CAUSE IN LANDSLIDES

factors leading to instablility of a given slope. reduce the shear strength and increase sheer stress of a slope: its OVERTIME THO.

TRIGGER IN LANDSLIDES

instantaneous event that causes the system to collapse!

EXTERNAL CAUSES OF MASS MOVEMENT IN LANDSLIDES

Factors outside of the slope that affect stability

1 SLOPE ANGLE:

2 UNDERCUTTING:

3 OVERLOADING:

4 VEGETATION

6 CLIMATE

7 ATMOSPHERIC RIVERS

SLOPE ANGLE AND LANDSLIDES

AN EXTERNAL CAUSE OF MASS MOVEMENT. You must have a slope to have mass movement, Steeper slopes = more movement

UNDERCUTTING AND LANDSLIDES

AN EXTERNAL CAUSE OF MASS MOVEMENT. The lower part of the slope is removed by roads, rivers, buildings, etc. which removes support

OVERLOADING AND LANDSLIDES

AN EXTERNAL CAUSE OF MASS MOVEMENT. Adding weight Caused by buildings, roads, landslides, trees, me, etc.

VEGETATION AND LANDSLIDES

AN EXTERNAL CAUSE OF MASS MOVEMENT. removing friction and sheer strength. roots soak up water as well. Roots bind loose material. Trees remove water for transpiration and mostly adds to slope stability.

CLIMATE AND LANDSLIDES

AN EXTERNAL CAUSE OF MASS MOVEMENT. If average temperature and rainfall is high: More water, Increased weathering/weakening of rocks, makes More fractures, More soil Etc.... | If average temperature is around 0° ... Freeze/thaw see internal causes. water expands after freezing and if the water gets into fractures of rocks, they can shatter and make MORE fractures! for ATMOSPHERIC RIVERS: have 2x volume idk we definitely are gonna pretend we know what this means

INTERNAL CAUSES OF MASS MOVEMENT IN LANDSLIDES

1 WATER CONTENT

2 MASS WASTING

3 FROST WEDGING/ FREEZE THAW

4 iNHERENTLY WEAK MATERIALS

5 QUICK CLAY

6 ADVERSE/BAD GEOLOGICAL STRUCTURES

WATER CONTENT IN LANDSLIDES

water, especially sediment: Adds weight (overloading) Decreases normal force/normal stress, which decreases friction and thus τf. Increases weathering and Acts as a medium for flows

different water content examples IN LANDSLIDES

UNSATURATED SOIL/DEBRIS VS SATURATED SOIL/DEBRIS MOIST IS GOOD. for example OVERLY WET SAND go plonk VERY LOW. DRY AF SAND GO small. SOME WATER! good. hoolds shape and has high angle of repose. while the others do not.

MASS WASTING IN LANDSLIDES

In solid rock: Water reduces shear strength along planes of weakness (fractures). infiltrates fractures, decreases friction, making material more likely to slide

FROST WEDGING/ FREEZE THAW IN LANDLSIDES

in colder climates, water gets into cracks and fracture. If it freezes it expands - forcing the fractures apart temperature and rock falls are inversely correlated- when temp goes down slides go up. temp goes up slides go down.

INHERENTLY WEAK MATERIALS IN LANDSLIDES

some are weak af. they fail at relatively/very low angles of repose. TWO EXAMPLES: volcanic rock (water can travel around volcanic layers easily, and store in there.) and clay (particle size. Clay minerals are often layered silicates in which layers are bound together and can swell in the presence of water as water is trapped between layers VERY absorbant)

QUICK CLAY IN LANDSLIDES

originally deposited below sea level and has salt in the matrix. Over time the salt is washed out which makes the clay very unstable so there is salt in between these divets, and the crystals are removed, causing collapse Quick clay slides not common, but very cool (and scary). can be moderate to fast landslides

ADVERSE/BAD GEOLOGICAL STRUCTURES IN LANDSLIDES

Unfortunate bedding/fracture orientation, weaknesses or structures within slope at an unstable angle/orientation.

TRIGGERS IN LANDSLIDES

A force or event that disrupts the equilibrium of a slope and initiates mass movement

SOME LANDSLIDE TRIGGER EXAMPLES: SHREVVELS J

- Snow melt

- Heavy Rainfall

- Earthquakes

- Rain on Snow

- Vehicles

- Volcanic Eruptions

- Excavation

- Loud Noises

- Skiing

- Jumping

LANDSLIDE CAUSE AND EFFECT

CAUSE: Reduces shear strength or increase shear stress

TRIGGER: Initiates motion

EFFECT: Fall, slide, flow, or complex movement

SOME COSTLY MITIGATION FOR LANDSLIDES

1 INVESTIGATION AND MONITORING: All of this is expensive! In some cases, especially very slow slides, it is cheaper to repair damage and ignore the landslide.

2 GEOLOGIC MAPPING: Map materials and properties on site => Predict type of failure. GLACIAL SEDIMENT: Rotational landslide more likely | IGNEOUS/METAMORPHIC rocks Without soil cover = rockfall/slide

3 LIDAR IMAGERY: a technique used to scan the surface topography of the Earth + 'sees through' trees. used to see where previous landslides have occurred.

3 MITIGATION FOR LANDSLIDES PAP

PREVENTION: do something to make sure landslides don't occur as often. Reduce probability of an occurrence.

AVOIDANCE: move to a different area, avoid problem.

PROTECTION: armour or strengthen the area that might be affected if landslides occur. Does not reduce probability of an occurrence.

AVOIDANCE FOR LANDSLIDES

a mitigation thin for landslides.

move to a different area, avoid problem.

SCENARIOS

- Buying all the property in a town

- Moving a completed highway

- Or convincing someone to leave a family home

PROTECTION FOR LANDSLIDES

a mitigation thin for landslides.

armour or strengthen the area that might be affected if landslides occur. Does not reduce probability of an occurrence.

1. ROCK BARRIERS: used to protect against rock slides where the rock is too weak to apply bolts

2. ROCK NET: Control where the hazard goes rather than prevent it from happening

3. ROCK FENCE: Catch falling/rolling rocks (lower slope angle than rock fall) dissipate kinetic energy

4. ROCKFALL SHED:

5. DEBRIS FLOWS RETENTION CENTRE: Debris Flow = Water + debris. It Remove debris from water and Control where the flow goes

PREVENTION FOR LANDSLIDES

a mitigation thin for landslides.

do something to make sure landslides don't occur as often. Reduce probability of an occurrence.

1. SLOPE REGARDING: very simple. Remove the material (somehow). Too expensive for many situations, but cheaper than avoidance. Pretty good for some rockfalls

2. SLOPES UNDERCUT WHEN BUILDING ROADS: Apply a resisting force at the bottom. RETAINING WALLS OR GABIONS

3. SLIDING ROCK: Apply rock bolts (rock anchors). Fs = resisting forces (Tf) / driving forces (T)

4. TOO MUCH WATER: Remove with drainage pipes

5. QUICK SOLUTIONS: Plaster with concrete

6. VEGETATION: Planting trees and shrubs (or Hydroseeding) to hold slopes together with roots.

EARTHQUAKE

the sudden and violent shaking of the ground, sometimes causing great destruction, resulting from the rapid movement along a fault in the Earth's crust. is the sudden release of elastic energy in response to a buildup of stressm that is released when elastic stresses exceed the strength of the fault, causing brittle failure

ENERGY OF EARTHQUAKE CAN BE RELEASED AS...

• Seismic waves: propagate through the Earth and cause ground shaking

• Deformation (fault displacement, rock fracturing)

• Heat

DIFFERENT FACTORS OF AN EARTHQUAKE I GUESS?

DRAMATIC: destruction of buildings, injuries, fatalities, tsunamis, landslides......

DISTURBING: what appears static and solid is moving violently

RISK: can be difficult to evaluate

FORECASTING: difficult in the short term

PREPARATION: possible but often expensive

WHERE EARTHQUAKES OCCUR

EDGES OF PLATE TECTONICS AND BOUNDARIES, The basic unit that moves is the tectonic (or lithospheric) plate, not the crust

FAULT

break in the rocks along which movement has occurred. Brittle fracture. Release of stored elastic energy → earthquake. Faults can be small....or large

TYPES OF FAULTS

NORMAL FAULTS

REVERSE FAULTS

STRIKE SLIP FAULT

WEGENER'S EVIDENCE

1. geological terrains along the continents.

2 DISTRIBUTION OF FOSSILS: Fossil ranges of organisms restricted by dispersal barriers are good indicators of connection of landmasses

3 EVIDENCE OF GLACIATION: Arrows indicate direction of flow of ice sheets, and they show antartica spreading across countries

WEGENER'S HYPOTHESIS AND WHY THERE WERE PROBLEMS WITH IT

Continents plowing through oceanic crust

Earth's rotation ("centrifugal force") pushing continents

Crumpling mountains where continents hit ocean crust

Scientists later rejected these because, the Oceanic crust is too strong and the Centrifugal force is far too weak

CONFIRMATION OF WAGNERS HYPOTHESIS

extensive sonar mapping of the sea floor revealed topographic features of the oceanic crust that were previously unobservable.

Harry Hess proposes seafloor was spreading, generated at the unusual ridges

Spreading Centers aka mid- oceanic ridges.

EARTH'S INTERIOR

CRUST: surface of area

LITHOSPHERE: consists of crust and upper solid mantle.

MANTLE: includes asthenosphere and

OUTER CORE: liquid.

INNER CORE: solid.

PLATE TECTONICS IS CONTROLLED BY

PHYSICAL PROPERTIES

· Composition

· Density

· Temperature

FORCES

· Gravity

DENSITY

mass / volume. units = kg/m^3

DENSITY OF ROCKS

Granite (continental crust) = 2,700 kg/m3

Basalt (oceanic crust) = 3,000 kg/m3

Peridotite (upper mantle) > 3,300 kg/m3

RHEOLOGY

When a solid material is put under stress, it will respond by deforming (undergoing strain)

3 TYPES OF DEFORMATION

ELASTIC: springs back, reversible

DUCTILE: 'plastic flow,' permanent

BRITTLE: breaks, permanent

DEFORMATION IS CONTROLLED BY

• Temperature, pressure

• Rate of deformation

• Duration of deformation

WHAT IS ELASTIC REBOUND THEORY

Stress builds in rocks as they deform elastically, then is released suddenly when the rock breaks, causing an earthquake. Seismic waves r realeased that why

STAGE 1: pre stress state. chill little rectangle

STAGE 2: Stressed rock deforms elastically. Energy is stored up over time as elastic deformation

STAGE 3: Energy is released suddenly by brittle failure and elastic rebound looks like two squares diagonal from each other. Post-rupture, unstressed rock Rupture surface (or fault plane)

WHAT IS DUCTILE DEFORMATION

Slow, plastic bending or flowing of solid rock without melting

DEFORMATION IN THE LITHOSPHERE (crust and uppermost mantle)

cool, solid, exterior shell. BRITTLE, but SOMETIMES DUCTILE

DEFORMATION IN THE ATMOSPHERE (mantle)

hotter/deeper, almost melting but still solid less than 5% melt. DUCTILE.

DEFORMATION IN THE MESOSPHERE (lower mantle)

hotter with high pressure, solid. STIFF BUT DUCTILE.

CONVECTION

the transfer of heat through the bulk movement of fluids (liquids or gases), driven by density and temperature differences.

WHAT DRIVES MANTLE CONVECTION

Heat from below and cooling at the top.

WHAT HAPPENS TO HOT MANTLE MATERIAL when going THRU MANTLE CONVECTION

It becomes buoyant and rises.

WHAT HAPPENS TO COOL MANTLE MATERIAL WHEN GOING THRU MANTLE CONVECTION

IT becomes denser and sinks.

HOW DOES LITHOSPHERE FORM THRU MANTLE CONVECTION

From hot, rising mantle material that cools at the surface.

WHY DOES LITHOSPHERE SINK THRU MANTLE CONVECTION

It cools, becomes denser, and gravity pulls it downward.

WHAT IS THE ROLE OF THE ASTHENOSPHERE IN CONVECTION

It is solid but very ductile, allowing mantle flow.

HOW IS CONVECTION RELATED TO PLATE TECTONICS

Plate tectonics is the upper part of the mantle's convection cycle.

EARTHQUAKE PREDICTIONS VS FORECASTS

Predictions = earthquake of a given magnitude will occur in a defined region within a specific period of time. Vancouver will be shaken by a magnitude 9 earthquake on Sept 19, 2027 between 2:00 and 3:00 PM

Forecast= more of a probability statement. eg. "There is a 10% probability of a magnitude 9 earthquake striking Vancouver in the next 50 years"

SOME FACTORS THAT GO INTO EARTHQUAKE PREDICTION RRRUUI

• Rapid ground deformation

• Rapid changes in the water table

• Radon emissions in wells

• Unusual electromagnetic disturbances

• Unusual animal behavior (?)

• Increase in seismic activity (foreshocks?)

.... have proven to be neither reliable nor repeatable

FLAWS ABOUT EARTHQUAKE PREDICTION

Specific earthquake predictions have almost never been successful. Many large earthquakes do not have foreshocks

EARTHQUAKE FORECASTING

- Applied stress is relatively constant (plate tectonics)

- Regional rock properties are relatively similar

- Application of statistics on the frequency of occurrence and magnitude could yield the likelihood or risk of an earthquake of a particular magnitude occurring in a given region.

- referred to as the Return Period or the Recurrence Interval

SUBDUCTION ZONE EARTHQUAKES

1. Earthquakes along the plate boundary (subduction interface)

2. Earthquakes within the subducting plate (JdF)

3. Earthquakes in the overriding plate (N America

SEISMIC GAPS

• "Possible" way to forecast earthquakes

• Patches along active fault zones that are seismically "quiet"

• Are these patches locked and potentially about to rupture?

Or maybe these patches are just creeping aseismically?

BC EARTHQUAKE EARLY WARNING SYSTEM

What can be done with an alert providing a few tens of seconds of warning?

1 Drop, Cover, and Hold on!

2 Open doors at fire stations and ambulance halls

3 Surgeons can stop delicate procedures

4 Stop traffic from going onto bridges or into tunnels

5 Stop aircraft landings at YVR

6 Stop or slow down trains

7 Shut down gas lines, ...

3 STEPS FOR BC EARTHQUAKE EARLY WARNING SYSTEM

1 PLAN AND PREP

2 SURVIVE

3 RESPOND AND RECOVER

1 PLAN AND PREP

1st step for BC earthquake warning system.

Assess and reduce risk.

Emergency management planning, practise

Harden infrastructure

Strict building codes

Retrofit or rebuild critical infrastructure

Hospitals, fire stations Bridges (disaster relief) Airport

Steady investment in all public buildings (Schools, community centres)

Develop, deploy early warning systems

Educate public

Secure your home, communication plan,

disaster supplies

2 SURVIVE

DROP down onto your hands and knees

Get under sturdy desk or table or crouch against interior wall

Triangle of life - no! Doorway - no!

COVER your head and neck

HOLD ON

Wait until shaking stops to get out

Turn off gas, water

West coast tsunami - seek high ground

3 RESPOND AND RECOVER

Search and rescue

Help the injured, get hospitals functioning

Relief supplies

Get airport and highways open

Restore essential services like Water, electricity, sewer

Telecommunications

Debris removal

Get our city up and running and Reconnect and rebuild our communities. Minimize economic disruption

WHAT IS PLATE TECTONICS

The unifying theory of solid Earth sciences explaining how Earth's lithospheric plates move and interact.

WHAT FUNDAMENTAL ROLE DOES PLATE TECTONICS PLAY

It controls Earth's structure and long‑term evolution.

WHAT HAZARDS ARE CAUSED BY PLATE TECTONICS

Earthquakes, volcanoes, and tsunamis.

WHAT TOPOGRAPHIC FEATURES RESULT FROM PLATE TECTONICS

Continents, mountain belts, ocean basins, trenches, and island chains.

HOW DO CONTINENTAL POSITIONS AFFECT CLIMATE

They influence winds, ocean currents, and global climate patterns.

WHAT RESOURCES ARE LINKED TO PLATE TECTONICS

Mineral resources, geothermal heat, and water resources.

WHAT IS THE CONTINENTAL CRUST

A granitic, thicker, less dense crust forming continents.

WHAT IS THE OCEANIC CRUST

A basaltic, thinner, denser crust beneath oceans.

WHAT IS THE ASTHENOSPHERE

A weak, partially molten layer of the upper mantle that allows plates to move.

WHAT IS THE RIGID MANTLE

The solid upper mantle layer that, with the crust, forms the lithosphere.

WHAT IS THE STIFFER MANTLE

A deeper, stronger mantle layer beneath the asthenosphere.

WHAT IS THE OUTER CORE

A liquid iron‑nickel layer responsible for Earth's magnetic field.

WHAT IS THE INNER CORE

A solid iron‑nickel sphere at Earth's center.

WHAT IS THE HYDROSPHERE

All water on Earth, including oceans, lakes, rivers, and ice.

WHAT IS THE ATMOSPHERE

The layer of gases surrounding Earth.

WHAT ARE EARTH'S COMPOSITIONAL LAYERS

Crust, mantle, and core.

WHAT IS THE CRUST MADE OF

Low‑density silicate rocks like granite, basalt, and sandstone.

WHAT IS THE MANTLE MADE OF

High‑density silicate rock, mainly peridotite.

WHAT IS THE CORE MADE OF

A dense iron‑nickel alloy.

WHAT DEFINES EARTH'S LAYERING

Differences in material density.

WHAT IS CONTINENTAL CRUST

A variable‑composition, lower‑density crust with densities around 2200-3000 kg/m³.

WHAT IS OCEANIC CRUST

A uniform, basaltic crust with density around 3000 kg/m³.

WHAT HAPPENS TO MANTLE DENSITY WITH DEPTH

It increases because pressure increases.

WHAT IS THE DENSITY OF THE MANTLE

Greater than 3300 kg/m³.

WHAT IS THE DENSITY OF THE CORE

Greater than 9700 kg/m³.

WHAT IS THE LITHOSPHERE

The cool, rigid outer layer made of the crust and uppermost mantle.