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Seismic Waves and Inversion Vandana Chopra Eddie Willett Ben Schrooten Shawn Borchardt. Topics. What are Seismic Waves??????? History Types of Seismic Waves. What are Seismic Waves ???. Seismic waves are the vibrations from earthquakes that travel through the Earth
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Travel along the earth's surface - similar to ocean waves
Primary or compressional (P) waves
a) The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave.
b) The P wave can move through solid rock and fluids, like water or the liquid layers of the earth.
c) It pushes and pulls the rock it moves through just like sound waves push and pull the air.
d) Highest velocity (6 km/sec in the crust)
I’m going to briefly cover three different Seismic wave equations
-Inhomogeneous Constant Density 2-D Wave Equation
-First Order Wave Equation
-Acoustic Wave Equation and how it’s
The pressure wave field is ψ and the seismic source is src(t)
Media velocity, C(x,z), the sound speed with x being the surface coordinate and z being the depth coordinate
Again the pressure wave field is ψ, the sound speed is c and x is the surface coordinate
Parameter α is determines the propagation direction of the wave
This is the simplest wave propagation model
Kronecker delta function
Considering small perturbations Δ in
And with Euler’s Equation with the viscosity equal to zero
And realizing P0 is constant and fb is negligible we have
The initial medium is at rest so Euler’s Equation can be changed to
eliminating the substantial derivatives.
Then we let the gradient of Φ be equal to the particle velocity
Next we assume the derivatives of space and time can be changed therefore
And removing the gradient operator on both sides gives us
Now the compressibility C and bulk modulus of K are defined in terms of a unit volume V and ΔV
The change in the change of fluid pressure P is now
Now computing the derivative of this equation with respect to time is
showing that the change in pressure is related to the change in density.
Then substitutions with this equation gives us
Now using the conservation of mass equation with the previous equation and time derivative gives us
Then using the time derivative again we get
We have the Acoustic Wave Equation
where is the speed of sound in the medium
1960; Nordquist, 1962; Eaton, 1969)
A multi-purpose / multi-physics parallel finite element
solver for the solid earth.
Seismological activity as of 4/4/2002
Talking Team #2
Some things seismic waves are good for include
·Mapping the Interior of the Earth
·Monitoring the Compliance of the Comprehensive Test Ban Treaty
·Detection of Contaminated Aquifers
·Finding Prospective Oil and Natural Gas Locations
·We Collect Information from the waves as they are reflected back to us and as they propagate to the other ends of the medium.
·What would happen if there was only 1 medium?
P wave Velocity (m/s)
S wave Velocity (m/s)
Glacial Till (Saturated)
The P and S wave velocities of various earth materials are shown below.
3-D Seismic Wave Propagation on a Global and Regional
Scale: Earthquakes, Fault Zones, Volcanoes
Information and Images Source: Prof. Dr. Heiner Igel
Institute of Geophysics, Ludwig-Maximilians-University, Germany
Whats the purpose of the accurate simulation of seismic wave propagation through realistic 3-D Earth Models?
·Further understanding of the dynamic behavior of our planet
·Deterministic earthquake fore-casting, assessing risks for various zones (i.e. San Francisco Bay Area)
·Understanding active volcanic areas for risk assessment
1.Parallelization and implementation of algorithms for numerical wave propagation on the Hitachi SR8000-F1
2.Verification of the codes and analysis of their efficiency
3.First applications to realistic problems
Before moving into 3-D the base numerical solutions had to be compared to analytical solutions for simple (layered) model geometries.
·Hitachi SR-8000 F1
·Typical Speed 750Mflops per node
·Internode Transfer Speed 1GB/s
·Numerical solutions to the elastic wave equations in Cartesian and spherical coordinates.
·Time dependent partial differential equations are solved numerically using high-order finite difference methods
·Space-dependent fields are defined on a 3-D grid and the time extrapolation is carried out using a Taylor expansion
·Space derivatives are calculated by explicit high-order finite-difference schemes that do not necessitate the use of matrix inversion techniques
·Fortran 90 coupled with the Message Passing Interface (MPI)
The parallel performance was tested with a code where all I/O was – as in production runs – carried out. An FD algorithm was run for 10 time steps on varying number of nodes.
Volcano topography in 3-D seismic wave propagation
1.The seismic signature of pyroclastic flows
2.Seismic sources inside magma chambers and volcanic dykes
3.Scattering vs. topographic effects as observed on Merapi
-In this project the first 3D calculation for the area in Germany with the highest seismic risk – the Cologne Basin – were carried out. The simulations show remarkably good agreement with observed data as far as the amplitudes for the ground motion is concerned which tells us that we are on the right way to be able to predict the possible ground motion amplification due to 3D structure for this (and other) areas.
- Subduction zones contain the largest earthquakes on Earth. Knowledge of there structural details not only is important for hazard assessment but also to understand the dynamics of subduction and mantle convection. In this project a 3D algorithm in spherical coordinates was implemented and earthquakes in subduction zones simulated. We were able to simulate particular wave effects observed in nature which – in the future – can be used to further constrain the structure of subduction zones.
- Fault zones (FZ) are though to consist of a highly localized
damage zone with low seismic velocity and high attenuation. The structure of FZs at depth has important implications for the size of (future) earthquakes and the dynamic behaviour of the rupture. Only recently it was observed that right above FZs a particular wave type (guided waves) can be observed which may allow imaging FZs at depth. Numerical simulations play an important role in developing imaging schemes and assess their reliability.
a. Wave Propagation in a heterogeneous spherical Earth (DFG, 2000-2002)
b. The seismic signature of plumes (DFG, 2001-2003)
c. The simulation and interpretation of rotational motions after earthquakes (BMBF, 2002-2005)
d. Numerical wave propagation in seismically active regions (KONWIHR, initially until 2002, may be further extended).
e. International Quality Network: Georisk (www.iqn-georisk.de) funded by the DAAD, 2001-2003. Will allow students, post-docs, professors from other countries to visit our Institute and take part in research projects. In combination with our simulation algorithms this may allow us to combine the numerical aspects with data from regions at risk. Involved countries: USA, Indonesia, China, New Zealand, Japan. The core of this network is a research group (1 post-doc, 3 PhD students) residing in Munich working of risk and hazard related problems in seismology and volcanology.
Brian W. Stump and D. Craig Pearson
Los Alamos, NM 87545
The cessation of testing of any nuclear explosive devices in all environments is the goal of the Comprehensive Test Ban Treaty. In order to assure compliance with such a treaty, an international monitoring system has been proposed. This system will include seismic, infrasound, hydroacoustic and radionucleide monitors located throughout the world. The goal of this system is the detection of any nuclear test.
The monitoring technologies that are included in the treaty are designed to detect a nuclear explosion in any environment and include seismic (50 primary and 120 auxiliary stations), infrasonic (60 stations), hydroacoustic (6 hydrophone and 5 T-phase) and radionuclide (80 stations) sensors distributed throughout the world (CD/NTB/WP.330/Rev.2, 14 August 1996). These sensors and the accompanying data would then become a part of the International Monitoring System (IMS) with the collation, analysis and dispersal of the resulting data and data products by an International Data Center (IDC).
Mining explosions generate both ground motion and acoustic energy that have some characteristics similar to small nuclear explosions, thus the proposed monitoring system may detect, locate and characterize some mining explosions.
In order to gain practical experience with the seismic component of worldwide monitoring, a series of empirical tests in the gathering, exchange and analysis of seismic data have been conducted under the auspices of the Conference on Disarmament in Geneva.
These tests have been titled the Group of Scientific Experts Technical Tests (GSETT) with the most extensive and recent test,
An example of a set of seismic stations that could be used for international monitoring of a CTBT. Primary stations are represented as circles and Auxiliary stations are represented as triangles.
Seismic waves that travel hundreds to over a thousand kilometers are classified as regional seismograms because they travel primarily in the earth's crust. Events that are only observed regionally are generally smaller than those observed teleseismically since the amplitude of the seismic disturbance decays as it propagates. The right part of Figure 2 illustrates the regional GSETT-2 triggers at Lajitas. It is interesting
to note that these smaller regional events occur primarily Monday through Friday and during working hours, suggesting that they are man made. This data suggests that a number of these regional signals may be associated with mining operations, in this case near surface coal extraction in Northern Mexico.
GSETT-3 included a greater number of seismic stations, continuous transmission of data and more detailed analysis of the data than GSETT-2. This experiment and the resulting data products allow further insight into the numbers and types of mining explosions that might be detected by regional seismic
The fifteen months of activity represented in Figure 3 suggests that in an active mining region such as the Powder River Basin, as many as several events per month might be expected.
Event location is very important in the assessment of the seismic data. Utilization of the arrival times of multiple seismic phases at a single seismic station, relative arrival times at an array of closely spaced seismometers, and observations at multiple stations are used to determine the origin of the events in space and time as well as some assessment of error in the estimates.
Figure 4: GSETT-3 events located in the Southern Powder River Basin compared to SPOT imagery and known locations of the events in coal mines in the region.
·5 Active mines outlined in Green Boxes
·Ellipses show GSETT-3 Detections
·Detections in many cases will associate with a region and not a specific mine with the GSETT-3
Large scale mining explosions, with the detonation of a large amount of explosives simultaneously, are observed at regional (100-2000km) and occasionally teleseismic (2000-10000 km) distances with seismic sensors.
As a result of the CTBT verification system, the largest of these events will have to be associated with standard mining operations to avoid the conclusion that the signal was created by a small nuclear explosion.
There is a need to implement techniques designed to reduce seismic amplitudes to reduce problems with the CTBT detection system.
Improved understanding of blasting practices and their effects on regional seismograms provides the opportunity for improved monitoring of a CTBT. Similarly, blasting practices designed to maximize explosive efficiency while minimizing ground motion within the mine are exactly those practices best for reducing both the size and ambiguity of regional seismic signals.
Wave Pictures and Movie Source
The GSETT3 Project
The 3D Seismic Wave Propagation Simulation Project
Addition Reading Recommended on mine blasting detection, monitoring of seismic waves caused by Blasting.
Black Thunder mine research with Los Alamos National Labs