Earthquakes and Tsunamis

fault

structure resulting from brittle deformation when different kinds of stress are applied → identified by hanging (head) & wall/foot wall and relative motion

normal faulting

type of faulting when hanging/head drops relative to footwall (result of tensile stress)

reverse faulting

type of faulting when hanging/head wall moves up relative to footwall (result of compressive stress)

thrust faulting

type of faulting when essentially a reverse fault at an angle, (result of shear stress)

strike-slip faulting

type of faulting that is nearly vertical, (result of shear stress) → either right-lateral or left-lateral (stand on one side of the fault and look across it, the opposite side appears to move a certain direction)

earthquake

sudden shaking of Earth's surface caused by the release of built-up energy of tectonic forces along a fault. released when stress overcomes friction, allowing the fault to slip.

elastic strain

explains how energy is stored → Earth's crust is constantly subjected to forces due to tectonic plate movements. Rocks on a fault experience stress, temporarily bending and deforming elastically instead of breaking

elastic rebound

stress exceeds the rock’s strength, the fault ruptures, and the stored elastic energy is released. rocks snap back to their original shape but in a new position. displacement occurs as released energy travels in seismic waves, causing ground shakes.

displacement

ground shifts along the fault after elastic rebound, which can be a few centimeters or several meters.

aftershocks

when surrounding crust readjusts to the new stress conditions after earthquake, smaller earthquakes in the same region that decrease in frequency and intensity over time

body waves

type of seismic waves consisting of P-waves and S-waves that travel internally in Earth, damaging but does not break buildings

surface waves

type of seismic waves consisting of Love and Rayleigh waves that travel on Earth’s surface → shaking and rolling waves that cause most earthquake damages

P-waves

type of body wave → particle motion and wave propagation are parallel, going in the same direction (compression in slinky)

S-waves

type of body wave → particle motion and wave propagation are perpendicular to each other, vertical motion but wave propagation is horizontal (snapping a rope tied to door)

Love waves

type of surface wave → propagate back and forth/side to side on surface

Rayleigh waves

type of surface wave → rolling waves across the surface

Recording seismic waves

See arrival of waves on seismometer → P (primary) waves arrive first, S (secondary) waves arrive second → time difference helps calculate the distance from the seismometer to the earthquake.

Triangulation

how to find the location of an earthquake → three seismometers knowing velocity and time of waves can inform distance and record the intersection of three circles of possible locations (epicenter)

Mercalli Intensity Scale

measures the size of an earthquake based on its effects on people, buildings, and the Earth's surface, qualitative, I to X

Richter Magnitude Scale

measures the size of an earthquake related to the maximum amplitude of the S wave from the seismogram → uses logarithims where M7 earthquake is 10x large than M6 → saturates after M7 due to seismic waves being too large

moment magnitude scale

related to the size of earthquake rupture area/fault plane, based on energy release, does not saturate like Richter Magnitude Scale

Ring of Fire

Rim of pacific ocean, where largest earthquakes occur

interplate earthquake

type of earthquake occurring at the boundary between tectonic plates

intraplate earthquake

type of earthquake occurring within the interior of a tectonic plate

shaking, landslides, liquefaction (solid starts behaving like a liquid), fire, disease, tsunamis

Causes of Earthquake damage

earthquake forecasting

scientists can forecast likelihood of an earthquake in a specific area over time → predicts number of times per century shaking from earthquakes will exceed 0.20g (significant damage to older buildings)

mid-ocean ridges

seismicity occurs at shallow depths, small earthquakes

convergent boundaries

seismicity occurs at deep depths, large earthquakes due to subduction and compression

transform boundaries

seismicity occurs at shallow to intermediate earthquakes due to shear forces

tsunamis

large wave produced by displacement of the sea floor; the displacement can be due to an earthquake, submarine landslide, or volcanic eruption

poor construction, mining, fracking, wastewater disposal

How Humans Affect Earthquake Consequences