Earthquakes in your Backyard Final Exam Study Guide

Flashcards covering vocabulary, tectonic theories, engineering concepts, and risk management strategies from the EPS 20 Final Exam Study Guide.

Annualized Earthquake Loss (AEL)

A long-term estimate of expected earthquake losses averaged over time based on hazard, exposure, and vulnerability, currently estimated at $14.7$ billion dollars for the United States.

Aristotle's Earthquake Theory

The ancient Greek proposal that earthquakes were caused by strong winds or gases trapped in underground cavities that shook the ground as they moved.

1906 San Francisco Earthquake

A magnitude $\text{~} 7.9$ event that led to the Lawson Report, which documented faulting and helped develop the elastic rebound theory.

Elastic Rebound Theory

A theory describing how stress builds up along a fault as tectonic plates move and is suddenly released when the fault slips, allowing the crust to snap back to a lower-energy state.

Seismology

The scientific study of earthquakes and the seismic waves that travel through the Earth.

Body Waves

Seismic waves that move through the interior of the Earth, consisting of P-waves (primary) and S-waves (secondary).

P-waves

Primary body waves where particles move back and forth in the same direction as the wave travels.

S-waves

Secondary body waves where particles move perpendicular to the direction of wave travel.

Surface Waves

Seismic waves that travel along the Earth's surface and typically cause the strongest shaking.

Kola Superdeep Borehole

The deepest artificial hole ever made, reaching about $12.26\,km$ in Russia, which barely penetrated the uppermost part of Earth's crust.

Seismometer

The sensor that detects and measures the motion of the ground during an earthquake.

Seismograph

The complete instrument that includes a seismometer and the system that records the motion.

Seismogram

The graph produced by a seismograph showing the arrival of seismic waves and ground shaking over time.

SF Bay Area Seismic Probability

A USGS estimate that there is a $72\%$ chance of at least one magnitude $6.7$ or larger earthquake occurring between 2014 and 2043.

Modified Mercalli Intensity Scale (MMI)

A ranking of shaking from I (not felt) to XII (severe destruction) based on observed effects and damage.

Directivity

A phenomenon where seismic energy is focused and amplified in the direction the fault rupture travels.

Hazard

The likelihood or probability of an earthquake occurring in a particular area.

Exposure

The people, buildings, infrastructure, and economic activities located in areas prone to earthquake shaking.

Vulnerability

The susceptibility of exposed people and assets to damage or harm, influenced by building design and preparedness.

Risk

The expected consequences of an earthquake (injuries, damage, losses), calculated as the product of Hazard $\times$ Exposure $\times$ Vulnerability.

Soft-story Failure

A structural failure resulting from the collapse of a weak ground floor, often seen in apartment buildings with parking on the first level.

Pancake Collapse

A building failure where floors collapse vertically onto one another.

Liquefaction

A process where water-saturated sediments lose strength and behave like a liquid during shaking, undermining foundations.

Cascading Failure

A chain reaction in urban environments where the failure of one infrastructure system (like roads) leads to the failure of others (like fire response).

HayWired Scenario

A USGS simulation of a magnitude $7.0$ earthquake on the Hayward Fault used to plan resilience for the Bay Area.

Alquist–Priolo Earthquake Fault Zoning Act

A 1972 California law that limits development directly across active faults to reduce surface rupture risk.

Active Fault (California Legal Definition)

A fault that has moved within the last $\text{~} 11,000$ years (the Holocene epoch).

Apparent Polar Wander

The observation that magnetic poles appear to have moved over time, providing evidence that continents themselves have drifted.

Divergent Boundaries

Plate boundaries where plates move apart and magma rises to create new crust, such as mid-ocean ridges.

Convergent Boundaries

Plate boundaries where plates move toward each other, leading to subduction or mountain building.

Transform Boundaries

Plate boundaries where plates slide past each other horizontally without creating or destroying crust.

Ridge Push

A driving force of plate tectonics where hot material rising at mid-ocean ridges pushes the plates apart.

Slab Pull

A driving force of plate tectonics where a cooling, dense oceanic plate sinks at a subduction zone and pulls the rest of the plate with it.

Anderson Classification: Normal Fault

A faulting regime where the vertical stress is the greatest: $S_v > S_{Hmax} > S_{hmin}$.

Anderson Classification: Strike-slip Fault

A faulting regime where horizontal stress is dominant: $S_{Hmax} > S_v > S_{hmin}$.

Anderson Classification: Reverse Fault

A faulting regime where horizontal stresses are both greater than vertical stress: $S_{Hmax} > S_{hmin} > S_v$.

Sag Ponds

Geomorphic features that form at releasing bends of a fault, indicating fault activity.

Aseismic Creep

Slow, steady movement along a fault that occurs without producing large earthquakes.

Seismic Tomography

A method that analyzes wave speeds through Earth’s interior to reveal structures like subduction zones, similar to a CT scan.

Moment Magnitude (Mw)

The standard scale for quantifying the size of an earthquake based on the total energy released.

Gutenberg-Richter Law

The principle that describes the relationship between earthquake magnitude and frequency; for example, magnitude 4 quakes are $\text{~} 10$ times more frequent than magnitude 5 ones.

Magnitude Energy Scaling

The energy released by an earthquake increases by roughly $32$ times with every one magnitude unit increase.

Run-up Height

The maximum vertical elevation above normal sea level that tsunami water reaches on land.

Inundation

The horizontal distance that tsunami water travels inland beyond the shoreline.

New Madrid Seismic Zone

A deeply buried fault system in Missouri that produced major (M8+) earthquakes in 1811-1812 within ancient continental crust.

Earthquake Early Warning (EEW)

A system like ShakeAlert that detects initial P-waves and issues warnings before the slower, more damaging S-waves arrive.

Induced Seismicity

Earthquakes triggered by human activities, such as wastewater disposal or fracking, which increase pore pressure and reduce friction on existing faults.

Electrical Resistivity Method

A geophysical method that measures how strongly the ground resists electrical current to identify groundwater or minerals.

InSAR

Interferometric Synthetic Aperture Radar; a satellite-based method that measures ground deformation with millimeter precision from space.

Resonance

When the frequency of ground shaking matches the natural frequency of a building, causing the amplitude of sway to increase dramatically.

Natural Period of a Building

The time it takes for a building to complete one cycle of motion, generally about $1$ to $2$ seconds for every ten stories.

Catastrophe (CAT) Model

Analytical tools used to estimate the financial impact of disasters by integrating hazard, exposure, and vulnerability components.

Reinsurance

A system where primary insurers transfer part of their earthquake risk to other companies to spread potential losses.