seismic anisotropy

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Solid Earth Geophysics- Geop503 Ali Oncel [email protected] .sa Department of Earth Sciences, KFUPM Seismic Anisotropy Reading: Fowler Chapter 8- Section 8.1

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Page 1: Seismic Anisotropy

Solid Earth Geophysics-Geop503

Ali [email protected].

saDepartment of Earth Sciences, KFUPM

Seismic Anisotropy

Reading: Fowler Chapter 8- Section 8.1

Page 2: Seismic Anisotropy

Summary: Lecture 6

Seismic Tomography

What does tomography reveal?

Types of tomography

Local Earthquake Tomography

Teleseismic Tomography

Data

Global Seismographic Network

Application

Global Seismic Tomography

Page 3: Seismic Anisotropy

Seismic tomography is a very active and popular research field …Then,

Seismic Imaging the Earth’s interior

• What is seismic/earthquake tomography?

• What information can it provide? 5-Minutes

Page 4: Seismic Anisotropy

1800’s view of Earth KRAEMER (1902)1903’s view of Earth

BOLT (Inside the Earth, 1973)

1973’s view of Earth DZIEWONSKI (~1990, from www)1999’s view of Earth

Progress in Knowledge of Earth

Page 5: Seismic Anisotropy

Lateral mantle structure

Page 6: Seismic Anisotropy
Page 7: Seismic Anisotropy

Global network for past 40 years

Page 8: Seismic Anisotropy

Data: Arrival Time

Travel 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

Page 9: Seismic Anisotropy

Modified from www.nanometrics.ca

1000 100 10 1 0.1seconds

Broadband Seismometer

1000 100 10 1 0.1seconds

Page 10: Seismic Anisotropy

South American Earthquake on Oct. 28, 1997, at 06 H 15 M, epicenter located at

4.3°S, 76.6°W, depth = 124 km, magnitude = 6.5

This map shows the location of the first of the three earthquakes considered in the lab. The lines connecting the earthquake to the stations are great circles on a global Mercator projection.

Earthquake located here

Source: EAS 388

Page 11: Seismic Anisotropy

Improvement in Seismic Stations

What is the nature of upwellings within the deep mantle?

Are there truly gaps in subducted slab within the lower mantle, as appears to be the case beneath East Asia?

Do slabs continue to the core-mantle boundary, if so, how?

What is the cause for the apparent difference in P and S velocity structure in the deepest mantle?

Better models are within reach, given the large amount of high quality seismic data becoming available. Such models can reduce uncertainty in plate reconstructions and can help resolve questions such as:

From: http://geo.web.ru/sbmg/sbor/tomography/Grand/grand.html

Page 12: Seismic Anisotropy

P-w

ave

S-w

ave

Global Seismic Tomography: A Snapshot

Page 13: Seismic Anisotropy

Map of Subduction Zones

PresentPast

Page 14: Seismic Anisotropy

Lower MantleBoth models show striking high wave-speed structures in the mid-mantle beneath the Americas and southern Eurasia.

The two models agree in detail for the anomaly beneath the Americas.The fast anomaly stretches from 30°S to about 50°N beneath the central part of North America.

FasterFaster

SlowerSlower