Seismic tomography uses seismic waves recorded from earthquakes around the world to image the interior of the Earth. During an earthquake, seismic waves travel through the Earth's crust and mantle, speeding up or slowing down depending on the type of rock. By analyzing recordings of these waves from multiple seismic stations, scientists can produce 3D models of seismic wave speed variations inside the Earth. These tomographic models provide insights into the composition and temperature of the mantle and help identify structures like subduction zones and mantle plumes. Improving coverage with more seismic stations results in higher resolution images of Earth's interior.

1. SEISMIC
TOMOGRAPHY

3. We can’t physically go inside the Earth. But we use imaging and
seismic tomography from earthquakes to see inside our planet.
During an earthquake, a break occurs at a fault. This is the driving
force that generates seismic waves through the crust and mantle. We
record each pulse at seismic stations from around the world.
Depending on the type of rock, waves either speed up or slow down.
If the rock is cold, waves travel quickly. But if rocks are hot, waves
travel slowly.
For every earthquake, we listen and record the seismic waves like a
tape recorder. From these seismology readings, we produce 3D
models of the Earth’s interior as a tomography.

5. This actual seismic
tomography
image shows a
cross section of
the crust and
mantle underneath
North America

6. Figure . Example of global tomographic results at different
depths.
Source : SEG wiki

7. Because of using few number of recording stations, few recorded
waves that pass through the structures inside the earth. But, by
increasing the number of the recording stations, it is able to get
much data and that will lead, in turn, to envision the shape and the
size of the structures in the tomographic results. ( Source : SEG )

8. Raypath’s coverage along North America continent

9. a) Block approach,
b) Grid approach
c) Boundary grid
approach
Model parameterization

10. The velocity at each grid node is regarded as an unknown parameter. By using an interpolation function, the
velocity perturbation at any point can be calculated.
where φ is latitude, λ is longitude, and h is the depth from the Earth’s surface; φi, λj, and hk represent the
coordinates for the eight grid nodes surrounding the point (φ, λ, h). Vm(φi, λj ,hk) is the velocity at the grid net
set for the m-th layer.

11. 3-D ray tracing algorithm
Forward modelling

12. Inversion
Because the data depends on the model parameters and the raypath geometry, tomography is non-linear
method. To make inversion, the tomography should be firstly linearized by using this equation d = Gm + e.

13. Resolution test
It's an important
understand the resolution
capability of the model
parameters. This is often
tested by constructing a
synthetic model.
Result of checkboard resolution test

14. • Interpretation of Earthquake Tomographic results
(Say Something)
• Applications of Seismic Tomography at some areas

15. Subduction zone Volcano

16. Oil and gas exploration by Seismic Tomography
Passive seismic tomography

17. Cross well seismic tomography

18. So far, seismic tomography has taught scientists that
Earth structure is more complicated than a simple
layered sphere divided into a crust, mantle, and core,
as depicted in many textbooks.
The mantle, for example, contains
materials of different compositions and
temperatures.
It holds plumes of rising hot rock and warped pieces
of
old oceanic crust and mantle that have been
subducted
beneath other tectonic plates. The images we have
now
of Earth’s interior are like blown-up pictures taken
from
early models of digital cameras. As more
seismometers
are placed on the surface to catch more seismic
waves,
the pictures are becoming sharper and scientists are
seeing more details. With these details, scientists are
making new discoveries about structures in Earth’s
interior, and with each new set of images, they are