3D Seismic Structure and Density
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Transcript of 3D Seismic Structure and Density
Solid Earth Geophysics-Geop503
Ali [email protected].
saDepartment of Earth Sciences, KFUPM
3D Seismic Structure and Density
Reading: Fowler Chapter 8- Section 8.1
Earth’s Density
To solve for we need a third equation.
Density from Seismology
Adams-Williamson-1923
(8.9)
(8.3) (8.11)
pp. 332-333 of Fowler’s Book
Gravitation Law: g(r)=GMr/r2
Mr => mass of Earth within radius r
g= 9.8 m/s**2, G=6.67x10**-11 Nm2kg**-2, r= 6371 km , M=5.97x10**24 kg
The (r) from Adams-Williamson self compression model (see Fig. 8.5 of Fowler, pp.335)
Density within the Earth
Song and Richards, Nature (1996)
Earth's Rapidly
Spinning Core
Origin of core structure
Composition of the core
Mineralogy of the inner core Temperature at Earth’s center.
Phase transition
ondulations
410 helps subduction
660 retards subduction
might cause temporary layering and avalanche
dp/dT of spinel – pervskite might be less negative than initially thought
3-D Seismic Tomography
Like a CAT scan
Reference: http://www.earth.northwestern.edu/people/seth/B02/lectures/Seismology/catscan.html
What is Tomography
TOMOGRAPHY ("SLICE PICTURE") USE BEAMS THAT TRAVEL THROUGH SOMETHING AT MANY DIFFERENT ANGLES COMBINE BEAMS FOR A DETAILED PICTURE OF VARIATIONS INSIDE
MEDICAL TOMOGRAPHY: X-RAYS (ELECTROMAGNETIC RADIATION) IMAGE VARIATIONS IN ABSORPTION DUE TO BONES, TISSUE ETC
CAT = COMPUTED AXIAL TOMOGRAPHY
By analyzing data from thousands of earthquakesSimultaneously a model of the internal velocity structure can be built upRequires super computers
Seismic tomography uses seismic waves with different ray paths to map three-dimensional velocity structure in the earth
Tomography
What does Tomography Reveal?
Tomography reveals differences in temperature and composition in the Earth
Tomography is now being used to map out:
regions of hotter and colder mantle
the movement of convection currents in the solid mantle
mountains and valleys on the Core-Mantle boundary
Local TomographyLocal Tomography Global TomographyGlobal Tomography
Definition
Source and receiver within the study are used to study 3D crustal studies
Sources are outside to study 3D mantle studies
Modified after from Dr. Stephan Husen’s lecture notes
What are the main differences between local tomography and teleseismic tomography?
Teleseismic Tomography
In teleseismic tomography sources (earthquakes) are outside the target volume. Receivers (stations) are located above the target volume.
Targets are structures in the upper and lower mantle, such as subducting slabs, plumes, continental roots, etc.
target volumestations
earthquakes
Modified after from Dr. Stephan Husen’s lecture notes
Global network for past 40 years
Data: Arrival TimeTravel time tomography uses first-arrivals of body waves (P- and/or S-waves)
Observation: Arrival time of first arrival
M4 earthquake close to Brugg, Station DAVOX
Modified after from Dr. Stephan Husen’s lecture notes