midterm 2

the blank is the geographic point at earths surface directly above the focus of an earthquake

epicenter

what three things should you do in the event of an earthquake

drop to the floor

hold onto a sturdy object to keep it from moving away from you

take cover under a sturdy desk or table

what cause the abrupt increases in seismic velocity illustrated at 410 km depth and 660 km depth

mineralogical changes in the structure of olivine

which factors influence intensity of shaving felt at earths surface during an earthquake

the depth to the hypocenter

near surface ground composition eg bedrock, sediment, artificial fill

density and age of underlying rock

true or false: richter magnitude is linearly related to the seismic energy released in an earthquake

false

what is the approximate thickness of the lithosphere

100 km

below is a plot of the hypsometry of Mars. from this plot what might you infer about the interior of mars

Mars does not have a differentiated crust with variations in rock density and/or crustal thickness

what type of seismic waves do the most damage to surface infrastructure during an earthquake

surface waves

a blank is an atom with a variable number of neutrons

isotope

which type of plate boundary experiences. megathrust earthquakes

ocean continent convergence

to be useful as a geochronometer radioisotope half lives should be approximately

10^9 years

true or false: earthquake science has now advanced to the point where we can accurately predict the day and magnitude of a future earthquake

false

what is the name for the time periods represented by the black and white rectangles in the geometric polarity reversal timescale

chrons

true or false: deformation is a synonym of metamorphism

false

true or false: a normal fault can violate the principle of superposition by placing older strata vertically above younger strata

false

rate or false: an absolute age is measured in years and typically involves a radiometer dating technique

true

which of the following brittle deformation features might you expect to find in a fault zone

pseudotachylyte

slickenfibers

fault breccia or gouge

true or false: radiometric dating of earth materials e.g acasta gneiss or jack hills zircons provides a maximum constraint on the age of earths formation

false.

what is our best estimate of the age of earth’s formation

4.54 Ga

what physical quantities do geophysicists use to image earths interior

heat flow

magnetic susceptibility

electrical resistance

seismic velocity

using the formulas for the velocity of p and s waves, explain why p waves travel through a fluid but s waves do not

shear modulus or rigidity of a fluid is 0

archimedes principle states that the buoyancy force exerted on a floating object is equal to the weight of the flutes displaced by the object

the application of archimedes principle to earths crust is called

isostasy

which scale measures the intensity of ground shaking during an earthquake

modified mercalli scale

true or false: reflected seismic waves bounce off the boundary between two materials with different seismic velocities

true

what are the SI units of stress

N/m²

the average geothermal gradient in the crust is 25 C/km but the average geothermal gradient in the mantle is 0.5C/km. how might to explain this change in gradient?

convection of the mantle redistributes heat more effectively than conduction in the crust

there are more heat producing elements e.g U, Th, K in the crust

what is the term of for a fracture in a rock on which there has been no appreciable movement

joint

which of the following a types of radioactivity used in radiometers dating

spontaneous fission

alpha particle emission

on a 1:24,000 scale map, 1 inch on the map is equivalent to what distance at earths surface

24,000 inches