CE 175: Introduction to Engineering Seismology

Vocabulary practice flashcards covering fundamental concepts, plate tectonics, fault types, seismic wave characteristics, magnitude and intensity scales, and near-fault ground motion phenomena from CE 175: Introduction to Engineering Seismology.

Earthquake Engineering

The application of a wide range of knowledge with the objectives of building cost effective structures that minimize the risk of injury or death after an earthquake.

Ductility

The capacity of a structure beyond yielding that is utilized in seismic structural design under a ductility-based approach.

Earthquake

The ground shaking caused by the sudden release of energy in the earth's crust, radiating outwards from the source and travelling in the form of seismic waves.

Plate Tectonics

The theory used to understand the causes of earthquakes and volcanic activities, establishing that earthquakes mainly occur at plate boundaries.

Spreading Ridge Boundary

A plate boundary where tectonic plates move apart as a result of molten rock (magma) rising to the surface and becoming part of the spreading plates.

Subduction Zone Boundary

A boundary formed when two tectonic plates collide and one plate plunges beneath the other.

Transform Fault Boundary

A plate boundary where two tectonic plates slide past each other without crustal volume change.

Intraplate Earthquakes

Earthquakes that occur within the interior of a tectonic plate, far from plate boundaries.

Pacific "Ring of Fire"

The seismically active belt of earthquakes, volcanoes, and tectonic plate boundaries surrounding the Pacific Ocean basin, accounting for $90\%$ of the world's earthquakes and $75\%$ of the world's volcanoes.

Fault

A fracture or zone of fractures between two blocks of rock, typically treated as a plane over short distances and described by its dip and strike.

Normal Faulting

Fault movement that occurs when the rock material above the fault plane (hanging wall) moves down, producing tension in the crust and horizontal lengthening of the ground surface.

Reverse Faulting

Fault movement that occurs when the hanging wall moves up relative to the foot wall, producing compression in the crust and horizontal shortening of the ground surface.

Strike-Slip Faulting

Faulting along often nearly vertical planes where adjacent crustal blocks slide horizontally past each other, producing large horizontal offset.

Body Waves

Seismic waves that travel through the interior of the earth, classified into Primary ($P$) waves and Secondary ($S$) waves.

Surface Waves

Seismic waves that travel along or near the ground surface, classified into Love ($L$) waves and Rayleigh ($R$) waves.

Primary Waves ($P$ Waves)

Compressional body waves that travel in the same direction as wave propagation, move faster than other seismic waves, and can propagate through solid, liquid, and gas media.

Secondary Waves ($S$ Waves)

Shear body waves that shake the ground back and forth perpendicular to the direction in which the wave is moving.

Love Waves ($L$ Waves)

Horizontal transverse surface waves that travel at the upper layers of the earth with particle motion orthogonal to the wave direction, occurring only if the surface layer has a wave velocity less than that of the underlying material.

Rayleigh Waves ($R$ Waves)

Surface waves that induce particle motion along a retrograde ellipse in the direction of wave propagation.

Focus (Hypocenter)

The point within the interior of the earth where the fault rupture process begins and from which seismic rupture propagates.

Epicenter

The geographic point on the earth's surface located directly above the earthquake focus (hypocenter).

Epicentral Distance

The distance measured across the earth's surface from any observation point to the epicenter of an earthquake.

Hypocentral Distance

The straight-line distance from any observation point on the earth's surface to the focus (hypocenter) of the earthquake.

Focal Depth

The vertical depth of the focus (hypocenter) of an earthquake measured from the earth's surface.

Earthquake Intensity

The severity of ground shaking at a particular location during an earthquake, assessed according to a graduated scale based on observed effects.

Modified Mercalli Scale

A non-mathematical intensity scale represented by Roman numerals ranging from imperceptible shaking to catastrophic destruction based on observed earthquake damage.

Earthquake Magnitude

A quantitative, seismologically evaluated measure of the total energy released and physical size of an earthquake event.

Richter Local Magnitude ($M_L$)

A scale developed in California by Charles Richter in 1935 for shallow local events ($< 600\text{ km}$ epicentral distance), defined as $\log_{10}$ of the maximum trace amplitude of a Wood-Anderson seismometer located $100\text{ km}$ from the epicenter.

Surface Wave Magnitude ($M_s$)

A worldwide magnitude scale based on the amplitude of Rayleigh waves with a period of about $20\text{ seconds}$, typically applied to shallow, distant ($> 100\text{ km}$) moderate to large events: $M_s = \log(A) + 1.66\Delta + 2.0$.

Body Wave Magnitude ($m_b$)

A worldwide magnitude scale for deep events calculated from the first few cycles of compressional ($P$) waves: $m_b = \log(A) - \log(T) + 0.01\Delta + 5.9$.

Seismic Moment ($M_0$)

A measure of earthquake size related to the work done during fault rupture, defined as $M_0 = \tau A D$, where $\tau$ is rupture strength, $A$ is rupture area, and $D$ is average slip.

Moment Magnitude ($M_w$)

An earthquake magnitude scale based on the seismic moment ($M_0$), given by $M_w = \frac{\log(M_0)}{1.5} - 10.7$, which does not saturate for large earthquakes.

Magnitude Saturation

The reduced sensitivity of ground motion parameters to earthquake size with increasing magnitude, which causes conventional magnitude scales to plateau nonlinearly.

Gutenberg-Richter Energy Relationship

The empirical relationship $\log(E) = 11.8 + 1.5M$ expressing released energy ($E$ in ergs), where a unit increase in magnitude equates to an approximate $32\text{-fold}$ increase in energy.

Aftershocks

Ground shakings that follow a major earthquake, decreasing in magnitude and frequency over time while posing severe threats to previously damaged structures.

Attenuation Models

Mathematical models that describe the relationship of ground motion parameters (such as maximum horizontal acceleration) to distance from the fault as a function of magnitude and fault type.

Peak Ground Acceleration (PGA)

The maximum absolute horizontal acceleration experienced at a specific site during an earthquake, derived from processed strong motion records.

Predominant Period of Motion

The period corresponding to the spectral peak of the Fourier amplitude spectrum, indicating the period component carrying the highest energy in the record.

Bracketed Duration

The total duration of ground motion that exceeds a specified threshold acceleration level, such as $0.05\,g$.

Near Fault Ground Motion

Ground motions occurring within approximately $15\text{ km}$ of a fault (per NSCP 2015) whose amplitude and frequency characteristics differ markedly from far-fault motions.

Directivity Effects

The arrival of seismic waves in a single, large, long-period pulse near the start of a record when the fault rupture propagates toward the site, with energy concentrated in the strike-normal direction.

Forward Rupture Directivity Effects

Near-fault phenomenon occurring when two conditions are met: the rupture front propagates toward the site, and the direction of slip on the fault is aligned with the site.