Midterm #1-Chapter 3 Flashcards
fracture
a general term for any breaks in rock
mainshock
largest EQ in a sequence
foreshock
smaller EQ that precedes mainshock (on the same sectipn of a fault)
aftershock
smaller EQs following a mainshock- can continue for years following the mainshock
seismology
study of EQs and the earth’s interior
seism
an EQ
arrival time
time when an EQ is detected by a seismograph
seismometers
instruments that detect earth’s motions
inertia
that property by which matter will remain at rest unless acted on by an external force
seismograms
records made by seismographs
wavelength
distance between two successive waves
period
the length of time for a complete cycle of waves to pass
hertz (Hz)
unit of frequency. One hertz equals one cycle per second
amplitude
maximum displacement above or below the undisturbed position (the height of a wave crest)
natural frequency
frequency at which a mechanical system (soil, a building) vibrates when disturbed
resonance
phenomenon when vibrations grow larger and larger
when earth shakes, it releases ____ that pass through the body of the planet
seismic waves
two types of seismic waves
body waves and surface waves
body waves
includes P (primary) and S (secondary waves)
surface waves
includes L (love waves) and R (rayleigh waves)
fastest waves are the
P waves
slowest waves are the
L waves
P waves
pass through solids, liquids, and gas, move in a pull-push motion
S waves
only pass through solids, move in a shearing motion
R waves
move in a backward rotating, elliptical motion (rocking boat motion)
L waves
move in a side-side, horizontal plane motion (similar motion to S waves)
isoseismal maps
map that shows the effects of the same EQ in different areas - demonstrating the different intensities
felt area
surface over which the EQ was felt by people
liquefaction
when strong EQ shaking causes solid sediments to transform into liquid
when soils are saturated…
soils loose strength and stiffness, which weakens their ability to withstand and support heavy loads
soft sediments vibrate at ____ frequencies
lower
hard sediments vibrate at ______ frequencies
higher
the greatest earthquakes in the world will occur where…
plate collide (convergent zones)
megathrust EQs
occurs when stress accumulates at subduction - dominated by shear stress… typically happen within 30 kms of the crust (shallow)
seismic gap method
theory that suggests EQs are expected next along the fault segments that have not moved for the longest time
world’s most famous fault:
San Andreas Fault (located offshore of San Fransisco)
locked zone
section of a fault that has not released seismic energy in a long time
creeping zone
section of a fault where energy is released frequently creating small to moderate EQs
what must designs for buildings in “EQ country” account for?
acceleration (the rate of change of motion)
the higher the magnitude of an EQ, the higher the ___
acceleration
retrofitting
strengthening pre-existing buildings (bracing it, infilling walls, adding frames to the interior or exterior, isolating it off the ground)
what scale are EQ’s effect on people and buildings assessed on?
the Mercali Intensity scale
