Earthquakes, Plate Boundaries, and Seismic Hazards

Vocabulary flashcards covering key terms, scales, instrumentation, historical seismic events, fault types, and geotechnical hazards from the engineering geology lecture notes.

Modified Mercalli Scale

An earthquake intensity scale ranging from I (Instrumental) to XII (Cataclysmic) based on observed physical effects and damage.

PHIVOLCS Earthquake Intensity Scale (PEIS)

An earthquake intensity scale tailored for local Philippine observations ranging from PEIS I (Scarcely Perceptible) to PEIS X (Completely Devastating).

Local Magnitude ($M_L$)

Also known as the Richter Scale, a quantitative metric calculated using trace amplitude ($A$) on a Wood-Anderson seismograph.

Surface Wave Magnitude ($M_s$)

A magnitude scale based on surface waves with approximately 20-second periods using maximum ground displacement ($A'$) and epicentral distance ($\Delta$).

Moment Magnitude ($M_w$)

A magnitude scale designed for large earthquakes to capture total rupture size using the seismic moment ($M_o$).

Seismic Moment ($M_o$)

A metric defined by the equation $M_o = \mu A_f D$, measuring total energy released via shear modulus, fault area, and average displacement.

Peak Ground Acceleration (PGA)

The maximum ground acceleration during earthquake shaking, expressed as a percentage or fraction of gravitational acceleration ($g$).

Seismograph / Seismometer

An instrument that detects and logs seismic wave arrivals ($P$, $S$, and surface waves).

Accelerometer / Accelerograph

A strong-motion sensor triggered by initial $P$-waves to record high ground accelerations without scaling out.

Tiltmeter

Monitoring equipment used to measure subtle changes in the inclination or slope of the ground surface.

Magnetometer

Instrumentation used to detect localized variations and fluctuations in Earth's magnetic field.

Dilatometer

An instrument used to monitor volumetric strain or pressure changes within rock or soil masses.

Scintillation Counter

Monitoring equipment used to measure radon gas emissions associated with crustal strain.

Resistivity Gauge

Equipment used to track changes in sub-surface electrical resistivity of rock and soil formations.

Creep Meter

An instrument deployed across fault lines to measure slow, continuous fault displacement.

Gravimeter

Equipment used to detect micro-changes in local gravitational fields caused by subsurface density shifts.

Surface Fault Rupture

Direct physical displacement and offset occurring along a fault trace at the surface during a major seismic event.

Regional Subsidence

Crustal downward deformation or lowering of the land surface, often occurring in extension zones or graben formations during faulting.

Tectonic Uplift

Crustal deformation resulting in the vertical displacement or elevation of land blocks along faults.

Liquefaction

A process where saturated, loose sand deposits undergo cyclic shearing under undrained conditions, causing pore water pressure to rise until effective stress drops to zero.

Sand Boils / Mud Spouts

Surface manifestations of liquefaction where pressurized sub-surface water and sand are forced upward to the surface.

Effective Stress ($\sigma'$)

The stress parameter controlling soil strength, which drops to zero during complete soil liquefaction ($\sigma' = 0$).

Lateral Spreading

A liquefaction-induced failure involving the lateral displacement of gently sloping soil blocks toward a free face.

Flow Slide

A severe slope movement where liquefied soil or loose material moves rapidly downhill as a fluid mass.

Rock Fall

Slope movement of rock masses occurring on steep slopes with minimum angles of $\ge 40^\circ$.

Rock Slide

Movement of rock blocks sliding down structural planes on slopes with minimum angles of $\ge 35^\circ$.

Rock Avalanche

Massive, high-velocity movement of broken rock fragments down slopes with minimum angles of $\ge 25^\circ$.

Rock Slump / Block Slide

Rotational or translational rock movement occurring on slopes with minimum angles of $\ge 15^\circ$.

Soil Fall

Rapid downhill collapse of soil masses on steep slopes with minimum angles of $\ge 40^\circ$.

Subaqueous Flow

Underwater soil movement capable of occurring on extremely gentle slopes with angles as low as $\ge 1.5^\circ$.

Soil Lateral Spread

Soil displacement that can occur on near-flat or very gentle slopes with angles as low as $\ge 0.3^\circ$.

Tsunami

Long-period ocean waves generated by large-scale vertical displacement of seawater due to submarine faulting, landslides, or volcanic activity.

Seiche

Standing waves generated within enclosed or partially enclosed bodies of water such as lakes, reservoirs, or bays during earthquake shaking.

1999 Chi-Chi Earthquake

A major Taiwanese seismic event ($M_w 7.6$) featuring vertical fault offsets up to 10 meters and extensive civil infrastructure damage.

1999 Izmit Earthquake

A Turkish seismic event ($M_w 7.4$) characterized by crustal stretching in the Gulf of Izmit and 3 meters of coastal subsidence.

1964 Niigata Earthquake

A Japanese earthquake ($M 7.5$) famous for extreme liquefaction and total bearing capacity failures of multi-story apartment structures.

1995 Kobe Earthquake

A major Japanese earthquake ($M_w 6.9$) that caused severe lateral spreading of caisson walls and port destruction on Port and Rokko Islands.

1971 San Fernando Earthquake

A US seismic event ($M_w 6.6$) that triggered a massive liquefaction-induced flow slide along the upstream slope of the Lower San Fernando Dam.

1920 Haiyuan Earthquake

A massive event in China involving over 650 loess landslides that resulted in more than 100,000 fatalities.

1970 Peru Earthquake

A catastrophic seismic event that triggered a glaciated rock avalanche which completely wiped out the city of Yungay.

1964 Prince William Sound Earthquake

A major Alaskan earthquake that produced massive, destructive landslides at Turnagain Heights and Government Hill.

Taiwan

Location of the 1999 Chi-Chi Earthquake ($M_w 7.6$).

Turkey

Location of the 1999 Izmit Earthquake ($M_w 7.4$).

Gulf of Izmit

Water body in Turkey that experienced crustal stretching and coastal subsidence during the 1999 Izmit event.

Gölcük

A coastal city in Turkey that suffered catastrophic submergence and flooding due to 3 meters of subsidence.

Niigata

Japanese city struck by a 1975 ($M 7.5$) earthquake, leading to classic foundation liquefaction failures.

Kawagishi-cho

Apartment complex in Niigata, Japan, famous for intact multi-story buildings overturning due to bearing capacity loss.

Kobe

Japanese port city impacted by a 1995 ($M_w 6.9$) earthquake that disrupted major port logistics through lateral spreading.

Port Island

Artificial island in Kobe, Japan, that suffered extensive lateral spreading and structural displacement in 1995.

Rokko Island

Artificial port facility in Kobe damaged by lateral movements and port crane collapses during the 1995 event.

Lower San Fernando Dam

An embankment dam in California, USA, whose upstream slope suffered a massive liquefaction flow slide in 1971.

Haiyuan

Region in China affected by the 1920 earthquake causing over 650 loess landslides.

Yungay

A town in Peru completely buried and destroyed by a glaciated rock avalanche triggered by the 1970 earthquake.

Turnagain Heights

A residential sub-division in Alaska that experienced extensive landslide devastation during the 1964 earthquake.

Government Hill

An area in Alaska damaged by massive earthquake-induced landslides in 1964.

Wu Shi Bridge

A bridge structure damaged by surface fault rupture during the 1999 Chi-Chi Earthquake in Taiwan.

Kuang Fu Elementary School

A school facility compressed and structurally failure-damaged by ground rupture in the 1999 Chi-Chi event.

P-Wave (Primary Wave)

High-speed seismic wave arrival that triggers accelerographs to start recording strong motion.

S-Wave (Secondary Wave)

Shear seismic body waves detected and recorded by seismometers.

Surface Waves

Seismic waves traveling along Earth's surface, used in calculating Surface Wave Magnitude ($M_s$).

Wood-Anderson Seismograph

Specific seismograph instrument calibrated to calculate Local Magnitude ($M_L$) or Richter Scale.

Trace Amplitude ($A$)

Measurement recorded on a seismogram used in the formula $M_L = \log(A/A_o)$.

$$A_o$$

Standard calibration amplitude factor used in the Local Magnitude ($M_L$) equation.

Ground Displacement ($A'$)

Measured in micrometers ($\mu\text{m}$), used to calculate Surface Wave Magnitude ($M_s$).

Epicentral Distance ($\Delta$)

The distance from an earthquake epicenter measured in angular degrees, used in the $M_s$ calculation.

Shear Modulus ($\mu$)

Material stiffness constant of rock, used in calculating seismic moment ($M_o = \mu A_f D$).

Fault Rupture Area ($A_f$)

Total area of the fault plane that ruptured during an earthquake, used in calculating $M_o$.

Average Displacement ($D$)

Average slip distance along a fault during an earthquake, used in calculating $M_o$.

$$a_{\text{m/s}^2}$$

Peak ground acceleration measured in meters per second squared, used in calculating PGA percentage.

9.81

Gravitational constant in $\text{m/s}^2$ used as the denominator in Peak Ground Acceleration (PGA) conversion.

Pore Water Pressure

Water pressure within soil voids that increases during dynamic shaking to induce liquefaction.

Bearing Capacity Failure

Structural foundation support loss resulting from soil strength loss during liquefaction.

Flotation of Utilities

Upward movement of buried light structures or pipes caused by the high density of liquefied soil.

Caisson Retaining Wall

Heavy quay wall structures at Kobe port that moved laterally and tilted during liquefaction.

Port Crane Collapse

Infrastructure failure resulting from lateral spreading of dock walls on Port and Rokko Islands.

Loess

Weak, wind-blown soil deposits in China that suffered over 650 catastrophic landslides in 1920.

100,000+

The number of fatalities caused by loess landslides during the 1920 Haiyuan Earthquake.

Glaciated Rock Avalanche

A slide containing ice and rock that buried Yungay, Peru in 1970.

Submarine Faulting

Undersea fault movement that displaces seawater volumes to generate tsunamis.

Volcanic Activity

Coastal or underwater volcanic eruptions that can act as a trigger mechanism for tsunamis.

Enclosed Bodies of Water

Lakes, bays, and reservoirs susceptible to standing wave oscillation (seiches) during earthquakes.

10-Fold Increase

The increase in seismic wave amplitude corresponding to a 1-unit increase in Richter Magnitude.

30-Fold Increase

The approximate increase in radiated seismic energy corresponding to a 1-unit increase in Richter Magnitude.

20 Seconds

Standard period of surface waves measured when determining Surface Wave Magnitude ($M_s$).

Radon Emission

Gas release monitored by scintillation counters to detect localized subsurface rock strain.

Strain Gauge / Pressure Gauge

Instruments like dilatometers used to track stress build-up within crustal formations.

Laser / Satellite Systems

Space-borne and optical monitoring technology used for large-scale deformation tracking.

Primary Hazards

Direct physical earthquake effects including ground displacement, fault rupture, and shaking.

Secondary Hazards

Cascading phenomena triggered by earthquake shaking, such as liquefaction, landslides, tsunamis, and seiches.

Alaska

Location of the 1964 Prince William Sound Earthquake that caused Turnagain Heights landslides.

Engineering Geology

Field applying geologic principles to plan, design, construct, and maintain civil engineering structures.

Primary Role of Engineering Geologist

Locates faults, evaluates fault activity, and assesses historical earthquake records.

Primary Role of Geotechnical Engineer

Determines soil and rock behavior under seismic loads to provide structural recommendations.

Design Earthquake

The anticipated earthquake used to calculate dynamic loading on a site.

Geotechnical Hazards Evaluated

Liquefaction, structural settlement, foundation stability, and slope failure.

Earthquake

An oscillatory movement of Earth's surface caused by a sudden release of energy.

Hooke's Law Equation

Expressed as $\sigma = E \epsilon$ for pure axial loading.

Elastic Strain Energy

Given by $U = \frac{\sigma \epsilon}{2}$ per unit volume.

Elastic Rebound Theory

Describes strain buildup in rock until fracture releases energy as seismic waves.

Focus (Hypocenter)

The interior point of initial rupture where seismic waves originate.