GEO 310 Midterm

Moho Boundary

Compositional boundary separating the crust from the mantle.

Lithosphere

Crust plus uppermost solid mantle; mechanically brittle, elastic, and rigid, forming tectonic plates.

Asthenosphere

Upper mantle below the lithosphere; ductile and fluid-like, allowing plate motion.

Outer Core

Liquid iron-nickel alloy layer that cannot shear and generates Earth's magnetic field.

Inner Core

Solid iron-nickel alloy layer due to extreme pressure.

Elastic Deformation

Instantaneous, fully reversible strain proportional to stress governed by Hooke's Law.

Brittle Deformation

Material fracture that occurs when stress exceeds yield strength, creating earthquakes in the lithosphere.

Ductile (Plastic) Deformation

Permanent, continuous deformation without fracturing under high temperature and pressure.

Divergent Boundary Signature

Moving apart, mid-ocean ridges, shallow/low seismicity, active basaltic volcanism, and positive gravity anomaly.

Convergent Subduction Boundary Signature

Moving together, deep ocean trenches, explosive volcanism, shallow-to-deep seismicity, and strong negative gravity anomaly at the trench.

Transform Boundary Signature

Sliding past, fault valleys, no volcanism, shallow high-magnitude seismicity, and neutral/variable gravity.

Curie Temperature of Magnetite

Approximately 580 degrees Celsius; the threshold below which cooling basalt locks in Earth's magnetic polarity.

Spreading Rate Math

Full spreading rate is 2v (double the single-side half rate v).

Euler's Fixed Point Theorem

Any motion of a rigid spherical shell is described as pure rotation around a fixed axis (Euler Pole).

GNSS Applications

Measuring millimeter-scale instantaneous or decadal plate velocities, monitoring fault locking and volcanic inflation.

P-Wave (Primary Wave)

Fastest body wave with longitudinal motion; travels through both solids and fluids.

S-Wave (Secondary Wave)

Slower transverse body wave that cannot travel through fluids (Vs = 0).

Rayleigh Wave

Surface wave characterized by elliptical retrogressive particle motion in a vertical plane.

Love Wave

Surface wave with horizontal transverse particle motion and no vertical component.

P-Wave Velocity Formula

Vp equals square root of (K plus four-thirds mu) divided by rho.

S-Wave Velocity Formula

Vs equals square root of rigidity (mu) divided by density (rho).

Surface Wave Dispersion

Phenomenon where surface wave velocity depends on frequency or period, with longer wavelengths penetrating deeper.

Free Oscillations

Whole-earth standing waves excited only by massive earthquakes greater than magnitude 7.5.

Spheroidal vs Toroidal Modes

Spheroidal modes change volume and shape; toroidal modes involve pure twist or shear with no volume change.

Seismogram Reading Order

P-wave arrival, followed by S-wave arrival, and finally surface waves.

Epicenter Triangulation

Method of drawing radius circles from at least three seismograph stations to find the earthquake epicenter.

Moment Magnitude (Mw)

An un-saturating magnitude scale based on physical fault properties rather than peak amplitude.

Seismic Moment Formula

M0 equals rigidity times fault area times average slip distance (mu * A * D).

Gutenberg-Richter Law

Log10(N) = a - bM, showing that an increase of 1 magnitude unit means tenfold fewer earthquakes occur.

Corner Frequency (fc)

Frequency from spectral analysis that is inversely proportional to fault rupture dimensions.

Focal Mechanisms ('Beach Balls')

Diagrams derived from first P-wave arrival polarities that split the focal sphere into quadrants using fault and auxiliary planes.

Strike-Slip Focal Mechanism

Four clean quadrants forming a vertical plus or 'x' layout.

Normal Fault Focal Mechanism

White or dilatational center quadrant indicating crustal extension and central tension.

Reverse Fault Focal Mechanism

Shaded or compressional center quadrant indicating crustal shortening and central pressure.