Natural Disasters: Exam 1 Review

(1) Natural Disasters Defined, (2) Earth Structure and Plate Techtonics, (3) Earthquakes, (4) Volcanism

Hazard

Thing or process with potential to harm humans and society

Natural Hazard Causes

Casualties, destruction of property, economic loss

Anthropogenic

Disasters that are caused by human action

Fast - onset

Minutes to hours

Slow - onset

Days to weeks

Stealthy

Decades or longer

Primary Disasters

Casualties and destruction caused by the natural hazard itself

Secondary Disasters

Hazardous events triggered by a primary disasters

Tertiary Disasters

Long - term societal disruptions following a disaster

Recurrence Interval

The average time between events of the same size

Annual Probability

The probability that a disaster of a specific size will happen in a given year

AP =

1/Recurrence Interval

Exposure

Potential for casualties, economic losses, social disruptions

Vulnerability

Potential for ability to minimize damage, ability to recover

Oceanic Crust

“Stong layer”, ~10km thick

Continental Crust

“Strong layer”, ~30 km thick

Mantle Lithosphere (upper mantle)

“Strong layer”, ~70km thick

Lithosphere

“Strong layer”, ~100 km thick

Asthenosphere (upper mantle)

“Weak layer”, ~300 km thick

How fast do tectonic plates move?

Few mm to cm per year

Divergent Plate Boundaries

Develop above zones of mantle upwelling; move away from eachother; volcanos and earthquakes

Convergent Plate Boundaries

Move towards oneanother; Volcanos and Earthquakes

Oceanic - Oceanic

Denser plate subducts under less dense

Oceanic - Continetal

Oceanic subducts under continental

Continental - Continental

Plates disappear and raise the land (under thrusting)

Transform Plate Boundaries

Plates slide past each other horizontally along a vertical fault (strike - slip)

Hotspots

Mantle plum below remains stationary where the plate above moves laterally - new volcanos

Earthquakes

Movement of Earth’s surface caused by propagation of seismic waves

Seismic Waves

Generated by the instantaneous disturbance of rock

Stick - Slip Theory

Stress builds up along a break in rock until the stress overcomes the strength and the rocks slip past each other (cake)

Elastic Rebound Theory

Describes how rocks deform as stress accumulates

Focus

Point at depth where a fault rupture initiates

Epicenter

The point on Earth’s surface directly above the focus

Body Waves

Waves that travel through the Earth

Primary Waves

Faster with a push/pull motion - through solid, liquid and gas

Secondary Waves

Slower with a up/down motion - thought solid

Surface Waves

Cause motion only in rocks near Earth’s surface (Rayleigh or Love waves)

Locating Earthquakes

Triangulation with 3 seismometer recordings to determine distance from seismometer to earthquake

Mercalli Intensity Scale

measure of the degree of shaking at any given location

Richter Magnitude Scales

Measure amplitude of largest wave, use nomograph to read magnitude, determine distance to epicenter

Amount of Energy Involved

Each increase by 1, energy released is 33 times greater

Moment Magnitude

Offset or displacement of fault rupture, area of fault rupture and rigidity of rocks

Shaking Intensity at a Site

EQ magnitude and acceleration, distance to focus, type of material, seismic wave directivity

Hazards

Surface rupture, ground motion, liquefaction (quicksand), landslides, fire, disease, tsunami

Mitigation of EQ

Geologists identify locations of risk, study before construction

Volcanism

Occurs at convergent and divergent plate boundaries

Magma

Liquid (molten) stale of rock

Lava

Magma that has erupted onto the Earth’s surface

How is magma created?

Slab dehydration, decompression melting, magma accumulation

Rhyolite Magma

Dome Volcano

Andesite Magma

Composite Volcano

Basalt Magma

Shield Volcano

Volcano Explosivity index

Classifies volcano eruption size based on volume of pyroclastic debris erupted

Pyroclastic Debris

Solid material ejected from during eruptions

Mafic

Magnesium and ferric, < 50% silica; low viscosity (BASALTIC) Divergent and Oceanic Hotspots

Intermediate

< 60% Silica, (ANDESTIC), Oceanic - Oceanic Boundary and Oceanic - Continental Boundary

Felsic

Feldspar and < 70% Silica, High viscosity (RHYOLITIC) Oceanic - Continental and Continental hot spots

Hawaiian

Continuous eruption of lava, slowly flows - shield volcanos

Explosive

Violent - lasts for hours or days followed by long periods of inactivity - stratovolcanoes

Hazards

Lava flow, pyroclastic flow, lahar, ash fall, volcanic explosion, bombs, gas

Lahar

Mixture of water, volcanic ash, and/or rock rapidly flows downhill - mud flow

Explosive eruptions are characterized by

Rhyolitic lava at low temperatures and high viscosity

Mitigate the impacts of natural hazards

Replacing parking lots with greenspace, securing gas-powered appliances

True or false: Seismicity (i.e., earthquakes) occurs at every type of plate boundary

True

Hotspot Volcanism

Occurs in the middle of tectonic plates

The fact that the Hawaiian Islands like along a line demonstrates that:

The Pacific plate has moved over a stationary hotspot

True or false: Designing buildings to collapse like a pancake such that the damage is not spread to other buildings is an engineering strategy to mitigate earthquake damages.

False

Which seismic typically has the lowest amplitude, and thus presents the lowest risk to human life and infrastructure?

P Wave

True or False: Deeper earthquakes tend to be less damaging because they are farther away from the land surface

False

Which part of the movie "San Andreas" was the most realistic:

Paul Giamatti stating that seismic amplitude increases by a factor of 10 as magnitude increases by a factor of 1