EARTHQUAKES AND SEISMICITY Flashcards
ORIGIN OF EARTHQUAKES
- elastic strain followed by a brittle faliure
- the ground deforms to accomodate stress, it releases to og position when released
tools to measure sesmicity
- ancient seismic sensor
- traditional seismograph
- sismometer
what scale is used for intensity
mercalli scale
magnItude
measure of total energy released
charles richter
types of seismic waves
- body waves; P and S waves
- surface waves
P waves
- horizontal vibration direction
- compression and expansion- dilation
S waves
- shear waves
- vertical vibration detection
- goes through only solids
- slower than P waves
surface waves
- form when waves reach the surface
- rayleigh waves- vertical
- love waves - horizontal
how to locate the focus
find nearest stations and plate boundries
* the interval between P and S arrival
divergent plate boundary
- spreading centers
- ridegs
- plates moving apart
convergent plate boundary
- subduction zones
- trenches
- plates smashing into eachother
transform fault
plates slide parallel to each other
1. dextral- right lateral
2. sinistral - left lateral
* san andres fault
what tells us about the eaths interior
refraction and reflection of waves
refraction
occurs where seismic velocity changes
s waves are attenuation
epicenter
A point on the Earth’s surface located vertically above the focus, or hypocentre, of an earthquake
MOHO
The boundary at the base of the Earth’s crust where seismic P-waves abruptly increase in velocity-
boundary of crust and mantel in lithosphere
* Occurs 10km deep beneath oceans, and more from continents
* not the base of plates
low velocity zone
- absorbtion of P waves
- represents the asthenosphere
hotspot
- isolated volcanic center in mid plate position, magma reaching the surface
- forms a chain of isnlands and seamounts as plate moves over it
mechanism of plate techtonics
convection
density driven circulation of material in response to temp gradients
* only process capable of driving plate movement
* dominated by cold slabs in the lithosphere
mechanism of plate techtonics
cold slab
apart of lithosphere
* move on top of asthenosphere by
* slab pull
* ridge push/slide
tectonics
non renewable resources
- used at a higher rate than they are returned
- have environmental impacts
renewable resources
- resources from atmosphere hydrosphere biosphere are used at flow rates less than natural cycles
- running water, food crops, wood, wind power, solar power
- have enironmental
non renewable resources
resources
- naturally ocurring accumulations of useful organic or inorganic material in concentrations and amounts that make extraction currently or potentially feasible
non renewable resource
reserves
resources that can be exploited economically
-under present conditions
spreading centers
- plates move apart at a mid ocean ridge
- asthenosphere rises adiabatically/w/o heat into the space
- decrease in pressure causes melting
- magma rises to surface and solidifies to form new crust, made of gabbro , mafic dykes and pillow lavas
rifting
continents splitting
EX east african rift
conventional hydrocarbon resources
geothermal heat on organic matter converts it to oil or gas
* it rises and accumulate in porus matter in sandstone or limestone
* it flows out when we drill into it
unconventional hydrocarbon resources
hydrocarbons trapped in impermeable mudstone or shale
* they dont flow out
continent - continent collision example and effect
himalaya and tibetan plateau
-collision doubles thickness of continental crust, whch can lead to partial melting = felsic magma
