Earthquakes Flashcards
What causes earthquakes?
- Associated with the breakage and displacement of rock, often along faults
- Kinetic energy is released as seismic waves
- Seismic waves radiate through the Earth’s interior resulting in “shaking” at the surface
How do earthquake location relate to plate boundaries?
Earthquakes are associated with plate boundaries
Several Types of Earthquake Hazards
- Ground shaking produces sediment liquefaction (instability of the ground), mass wasting (landslides), and damage to buildings and other structures
- Fires following earthquakes can be catastrophic and fire-fighting capabilities may be compromised
- Often water lines and emergency equipment are damaged and utility and communications systems are disrupted
- A tsunami may be generated
Explain how an Earthquake could lead to flooding
- Divert rivers
- Mass wasting into water
- Liquefaction
The Elastic Rebound Theory (brittle deformation)
- Explains the origin of earthquakes
- Energy is stored in the form of elastically deformed rock. When the strain exceeds the strength of the rock it breaks and the energy is released
Strain Release
Eventually the rock is no longer able to accommodate the buildup of strain and it ruptures, either along a pre-existing fault or at a new location
Focus
where the rocks actually break, where energy is released from, can be at surface or 700km depth
Epicenter
point at Earth’s surface directly above the focus, focus and epicenter may be at the same place but not common
Clusters
Earthquakes tend to occur in clusters, in both time and space
Intraplate Earthquakes
Most seismicity occurs at plate boundaries, but intraplate earthquakes are common
Divergent, Convergent, and Transform Margins
- Are sites of frequent earthquake activity
- Poorly understood
- Most have shallow foci
- Tend to occur in soft, weak areas of plate interiors, caused by stresses transmitted from plate boundaries
- Reactivation of old rift zones or faults
- Hot spots
Divergent Seismicity
Earthquakes occur in shallow crust b/c that’s all there is
Convergent Seismicity
Zone of seismicity along plane of subduction zone is called Wadati-Benioff Zone
Earthquakes Produce Four Types of Seismic Waves
Two types of Body Waves (within crust) and two types of Surface Waves (surface duh)
Types of Body Waves
P-wave: fastest, solid/liquid, push/pull (compression/extension) motion
S-wave: 2nd fastest, solid only, side to side
Types of Surface Waves
Rayleigh wave: 3rd fastest, surface, up/down forward/back motion
Love wave: slowest, surface, side to side motion
Liquids do not resist changes in shape
Rather, they absorb S waves instead of transmitting them
Speeds of these waves allow us to
locate Earthquakes
Further away from the foci, the larger the
gap between P and S waves, and vice vera for closer
Seismometers
Instruments that measure and help locate earthquakes
Could an Earthquake be located with only 2 seismic stations?
No, need at least three to triangulate location of the earthquake
Earthquake Magnitude
Expressed as whole number and a decimal fraction = Richter scale
Modified Mercalli (MM) Intensity Scale
- Intensity expressed using MM Intensity Scale
- Scale is how much of humanity’s stuff got fucked up
Difference Between Intensity and Magnitude?
Intensity is qualifiable, also depends on how prepared certain areas are, and magnitude is quantifiable
There is also no focus on assessing the damage since everyone is focused on saving lives after the earthquake.
Seismology
- Study of seismic waves in order to improve our understanding of Earth’s interior
- Wave infraction is used to identify a discontinuity
Seismic Data confirms:
the existence of discontinuities in Earth’s interior
Mohorovicic Discontinuity
- the boundary between the Earth’s crust and the mantle
- ~8km beneath oceanic basins
- ~20-70km beneath continents
Seismic Tomography
Uses seismic data from hundreds of seismic stations and hundreds of different earthquakes to provide a 3-D seismic velocity image of Earth’s interior
