3d seismic structure and density

Solid Earth Geophysics-Geop503

Ali Onceloncel@kfupm.edu.

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