GEOP 341 Final

What determines seismic resolution?

The distance between adjacent peaks or troughs - depend on high frequency content

When a seismometer measures ground motion,

The heavy mass tends to stay stationary due to inertia The frame tends to shake with ground together

Magnetic anomaly may be used to distinguish an igneous rock body and a salt dome at depth because ______

The igneous body typically produces a strong magnetic anomaly

To determine paleolatitude of a rock sample in paleo magnetic studies, one needs to measure ______

The inclination of remnant magnetization of the rock sample

Critical distance Xc

The shortest source receiver distance for observed refracted wave - no refracted arrivals within this time Xc = 2htan(0c)

At the critical distance, travel-time curves of refracted wave Tr(x) and reflected wave Tf(x) have the following relation

Tr(x) is tangent to Tf(x)

Apparent velocities from travel time curves in exploration seismology may give us velocity values of some rock layers

True

In seismic data processing, stacking velocity is typically root mean square velocity

True

Magnetic anomaly is more complex than gravity anomaly, and the same magnetic body may produce different magnetic anomalies at different magnetic latitudes

True

P wave radiation pattern tells us that first motion at a seismic station is ____ if the station is in the compression quadrant

Upward

PKJKP

Wave refracted through the mantle and outer core as P energy - converted to s energy in inner core, then back to P at surface

Chemical Remanent Magnetization

When ions precipitated from solution to form ferromagnetic minerals (hematite)

thermoremanent magnetization

When rocks, usually with magnetite, cool below Curie

Detrital magnetization

settling sediments align with poles

The magnetic inclination is the angle that a compass needle makes with

A horizontal ground surface

Diffraction from a point source shows as _______ on an unmigrated seismic section

A hyperbola with a greater curvature and 2 branches

Hypocenter

A point on fault surface where rupture starts

Epicenter

A point on grounds surface directly above hypocenter

Intermediate and deep earthquakes can occur at a _____ boundary

Convergent

On an unmigrated seismic section, a dipping interface connecting 2 horizontal interfaces will ______

Cut the deeper interface and leave a gap from the shallow one

Travel time curves of ____ are straight lines

Direct waves, refracted waves

Apparent velocity

Distance between 2 closely spaced receivers/difference in travel time Vap = 1/slope of T(x) travel time curves

Which statement about rock magnetization is correct?

Induced magnetization occurs only if an ambient field is present

Which statement is correct about the origin of the Earth's magnetic field?

It is mainly caused by some internal processes within the earth

S wave shallow zone is caused by

Liquid outer core

S-wave shadow zone is caused by

Liquid outer core

diamagnetism

Negative, opposite, weak, halite

If the stacking velocity is too slow, NMO will give you _____

Over correction

When you perform NMO, if you use a velocity that's too low, a station with a larger source receiver distance will be ____

Over-corrected, meaning reflection at station comes too early after NMO

In which type of wave is the particle motion direction parallel to the wave propagation direction?

P wave

Which type of wave has particle motion parallel to wave propagation direction?

P wave

In studying seismic phases, K and J represent _______ and _________ respectively

P wave in outer core - S-wave in inner core

PcP

P wave reflected off the outer core

PKP

P wave refracted from mantle, through outer core, then back through mantle

PKIKP

P wave refracted from mantle, through outer/inner, back out

PP wave

P wave refracted through mantle, reflected at surface then retracted again

If a P-wave encounters an interface of 2 rock layers with different velocity what would happen?

Part of the energy would be reflected and part will be refracted

To interpret seismic refraction record for subsurface geologic models, one needs to

Pick a direct and refracted wave arrivals Measure slopes and T-axis intercept times of travel time curves of direct and refracted wave arrivals

Ferromagnetism

Positive, strong, metallic

Paramagnetism

Positive, weak, sandstone

SV waves are best seen in _______ components of seismographs

Radial

What determines seismic definition?

Ratio of amplitude of main lobe to adjacent side lobes - depends on bandwidth, broad enough to detect a layer

For the reversed refraction profile of a dipping interface, which statement below is NOT correct

Reciprocal times are different

Comparing travel time curves of direct and refracted waves, we have a crossover distance Xcr. At source-receiver distance beyond Xcr, which wave arrives earlier?

Refracted wave

Which of the following seismic resolution and definition is correct?

Resolution depends on high frequency contents, while definition depends on broadness of bandwidth in seismic waves

ScS

S wave reflected off the outer core

SSS

S wave reflected twice at surface

Why input seismic signals are important in seismic reflection surveys?

Seismic signals include amplitude and frequency content info - useful to infer composition and other properties of rocks

Which elastic property of rock best describes the ability for rock to resist shearing?

Shear modulus

S wave velocity of a rock is determined by the rock's

Shear modulus and density

To infer seismic velocities of subsurface rock layers from a seismic refraction record, we primarily make use of _____ of travel time curves

Slopes

In a spring slider model, when the stiffness of the spring increases, the sliding behavior of the system tends to be _______

Stable

For a dipping planar interface, after migration, the interface becomes _____, compared with before migration

Steeper and shorter

What happens during and immediately after a large earthquake?

Stored elastic energy is released Rock goes back to stress free status with offset Seismic waves are emitted and propagate in the Earth

Travel time equation

T = 2h/V1

Travel time curve of reflected waves is _____ to that of refracted waves at critical distance, and is ____ to that of direct waves at large distance

Tangent, asymptotic

Which statement about Vp and temperature (T) of the uppermost mantle for the given tectonic setting is correct?

High Vp and low T beneath Rocky Mountains

Internal sources of geomagnetic field

- crustal: short wavelength variations (remnant, induced magnetization) - no mantle - core field, 90% of earth's field

How does total field intensity vary with magnetic latitude?

- increases with magnetic latitude? -

External sources

- solar origin - weaker, variations on shorter times - magnetic field generated by outer core flow

an earthquake of magnitude 8 releases _______ times of energy and generates _______ times of amplitude of ground motion at the same source distance, compared to a magnitude 6

1000 - 100

For a typical Continental area, if one wants to conduct a seismic refraction survey to study Moho depth and uppermost mantle velocity of the region. What is a reasonable range of spread length for the survey?

175-350km

Amplitude equation

Ar = (Ai)(RC) Ar = reflected wave Ai = incidence wave

For a given sedimentary rock layer, if frequency of seismic waves propagating within it increases, then wavelength of seismic waves will

Become shorter

A beach ball diagram for a thrust faulting earthquake shows

Black surrounded by white

If a material undergoes no volume change under compressive stress then which if it's elastic properties is infinite?

Bulk modulus

When stress applied on a rock body is removed, the body does NOT return to its original shape and volume. The rock body likely experienced ______ deformation

Ductile

NMO correction is to remove

Effects of offset between source and receiver in a CMP gather

Earth's magnetic field is a vector field and it's direction is described by the strike and dip angles

False

Fluid injection, in particular waste water disposal, may have induced felt earthquakes in the DFW area, because fluid injection causes a decrease in pore pressure around a fault, reducing fault strength to resist shear sliding on the fault

False

Friction on an interface between 2 bodies is due to the real contact area being equal to the surface area of the interface

False

Magnetic storms, which are an example of secular variations in Earth's magnetic field, are caused by variations in solar wind

False

Reflection coefficient can only be positive

False

Why do we want to find out CMP gathers from shot gathers in reflection seismology?

For stacking to enhance signal to noise ratio