Transcript
Solid Earth Geophysics-Geop503
Ali Onceloncel@kfupm.edu.
saDepartment of Earth Sciences, KFUPM
Seismic Anisotropy
Reading: Fowler Chapter 8- Section 8.1
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
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
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
Lateral mantle structure
Global network for past 40 years
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
Modified from www.nanometrics.ca
1000 100 10 1 0.1seconds
Broadband Seismometer
1000 100 10 1 0.1seconds
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
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
P-w
ave
S-w
ave
Global Seismic Tomography: A Snapshot
Map of Subduction Zones
PresentPast
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
top related