In the first and second year of my study, we analyzed the core reflected waves (PcP and ScP) to study the small-scale structure on the top of the core mantle boundary (CMB). These waves are collected from the WOMBAT transportable array of short period stations in southeast Australia and WRA short aperture array of broadband stations in Northern Territory. We have examined and identified 34 events with clear onsets of ScP- waves among the waveforms of more than 1000 (6.5>Mw>5.0) events originated from the west Pacific subduction zones. The presence of small-scale structures slows down and speeds up the seismic waves and produces the pre- and post- cursors of the ScP- waves. Post- and pre- cursors are distinguishable after the deconvolution of PcP from ScP- wave, isolating the source and path effects. We further utilized a conventional forward waveform modeling of these waveforms to investigate the physical properties of such structures. However, we find that the forward waveform modeling is highly non-unique specifically due to trade-off between the layer thickness and S-wave velocity.
In response, we developed a rigorous Bayesian inversion. Sampling of the Posterior probability density (i.e., the solution to the Bayesian inverse problem) is based on the interaction of a multiple Markov-chain (i.e. parallel tempering) using parallel computing on a supercomputer. Probabilistic condition is imposed to accept or reject the random perturbations. In addition, any two random chains are allowed to interchange between each other with certain probability so that the chain can escape from the local energy minima of parameter space. After we demonstrate the feasibility of the method through various synthetic experiments, we applied to the S...
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...We are now able to validate both methods through synthetic experiments. We are now applying both two steps linear inversion and NA for observed normal mode data. Once we are able to calibrate our results, we implement more sophisticated and rigorous hierarchical Bayesian inversion to estimate the 3-D structure. The hierarchical Bayesian inversion will reduce the subjective choice on the selection of quality receiver strips. We can estimate not only the uncertainties in 3-D structures but also the noise in the data. The noise in the data will be relaxed as a free parameter in the inversion. Knowing the noise in the data will constrain the level of fit, and this will help accurately quantify Earth's 3-D structure. Finally the temporal change in the splitting functions for inner core sensitive modes will allow us to measure the differential rotation of the inner core.
Smith, I. E. M., Price, R. C., Stewart, R. B., and Worthington, T. J. (2009). An assessment of the mantle and slab components in the magmas of an oceanic arc volcano: Raoul Volcano, Kermadec arc. Available: http://researchcommons.waikato.ac.nz/bitstream/10289/2685/1/Price assessment.pdf. Last accessed 10th Jul 2011.
Watson, J 2012, Pangaea, Earthguide at Scripps Institution of Oceanography, Virginia, Viewed 11 April 2013,
Earths mantle is mainly composed of substances high in iron and magnesium. The melting point of every substance depends on the pressure and the deeper we go the higher the pressure becomes. Because of this the upper mantle is said to be semi-molten and the lower mantle solid. The upper mantle iron-substances are semi-molten because it is hot and they are under little pressure, lower mantles iron-substances are solid because they are under a lot of pressure. The mantle is 35 to 2890km.
Making a good and persuasive argument is very much an acquired skill. It requires much practice and perfecting. It takes more than just having passion and making good points. Just because a person is passionate about the topic or has supporting details does not mean they can make a successful argument. Much more thought and skill is required. Gordon Adams, in his letter to the Arizona State University standards committee, demonstrates this quite well. Gordon Adams writes a passionate argument, yet his argument lacks several critical aspects.
However, the peak fault slip was to the north of the epicenter- not where was expected to
Our understanding of the Earth’s interior has been a focus for scientific study for multiple decades, recognised in the early 1900’s. Throughout the years, scientists have debated and quarreled over their findings, observations and theories for the most correct model of the composition and internal structure of the Earth.
Beno Gutenberg was the foremost observational seismologist of the twentieth century. He combined exquisite analysis of seismic records with powerful analytical, interpretive, and modeling skills to contribute many important discoveries of the structure of the solid Earth and its atmosphere. Perhaps his best known contribution was the precise location of the core of the Earth and the identification of its elastic properties. Other major contributions include the travel-time curves; the discovery of very long-period seismic waves with large amplitudes that circle the Earth; the identification of differences in crustal structure between continents and oceans, including the discovery of a significantly thin crust in the Pacific; the discovery of a low-velocity layer in the mantle (which he interpreted as the zone of decoupling of horizontal motions of the surficial parts from the deeper parts of the Earth); the creation of the magnitude scale for earthquakes; the relation between magnitudes and energies for earthquakes; the famous universal magnitude-frequency relation for earthquake distributions; the first density distribution for the mantle; the study of the temperature distribution in the Earth; the understanding of microseisms; and the structure of the atmosphere.
The Tohoku earthquake caused by the movement of the Pacific plate slides underneath the Eurasia plate at the rate of three inches per year, associated with Japan Trench (NOVA, 2013). There is a debate whether the plate involved with the Pacific plate was the fragment of the North America plate because this
Iceland is known as the best studied, large-volume, active volcanic region in the world. It features the largest exposure of any hotspot at a spreading ridge, and is possibly attributed to a thermal plume in the mantle. Spanning the Mid-Atlantic Ridge, Iceland was first appearing over the ocean surface about 16 to 18 million years ago. The current plate boundary consists of a series of volcanic and seismic zones (Fig. 1) that have developed and reorganized in a complex manner due to interaction of Iceland Mantle Plume.
The epicenter of the earthquake in Alaska was about 10km east of the College Fiord, approximately 90km west of Valdez and 120km east of Anchorage, Alaska largest city. The earthquake was felt about 1,300,000 square kilometers away from the epicenter. (Christensen, Doug PhD.) About 30 kilometers deep, the first slip occurred under northern Prince William Sound, and an 800 kilometer rupture in the rocks extended horizontally, roughly parallel to the Aleutian trench. (Bolt) The cause of this massive earthquake was the vertical displacement of northwest motion of the Pacific plate. Also, it was estimated that about 200,000 square kilometers of the crust were deformed, making this the greatest area of vertical displacement ever measured. (Bolt)
We know that the molten rock material called magma is found inside the earth as we have seen it coming out through volcanoes.
There are four different types of seismic waves: Primary (P), Secondary (S), Love (L) and Raleigh (R). P waves are the first waves to reach recording stations, which is why they are called primary waves. They travel at approximately 20,000km/h and are a push-pull wave, which means they stretch and squeeze rocks as they pass through. S waves are slower than P waves, travelling at 10,000km/h, therefore arriving after P waves at the recording station. They have larger amplitudes th...
The first study of earthquakes came in the 18th century after five earthquakes in England and a massive earthquake in Portugal. The idea of plate tectonics did not come for another half century ultimately providing a deeper explanation of earthquakes. Gaining further insight to the current explanation of earthquakes that are truly caused by the stress along active plate boundaries where tectonic plates converge or slide past each other relieving stored stress along the fault lin...
Towards the north, the Pacific Plate is moving to, as well as it is being subducted below the Australian plate. Towards the south, these two plates are moving towards each other, but the Australian Plate is being subucted under the Pacific Plate. The motion of these plates is quite small but rapid, which is regularly accompanied by a series of earthquakes. In the northeast section of the fault, there is a seismic zone where deep earthquakes occur. This occurs where the Pacific Plate is subducted under the Australian Plate. In this area, the boundary between both plates known as the Benioff Zone is located. Shallow earthquakes occur towards the southeast of this seismic zone. On the other hand, towards the south, where the Australian Plate is being subducted, deeper earthquakes occur on the southeast section of the seismic zone (UO).
The concurrent convective circulations in the mantle leads to some segments of the mantle moving on top of the outer core which is very hot and molten in nature. This kind of movement in different segments occurs as tectonic plates. These tectonic plates are basically seven on the earth surface as major ones, although, several small ones exist also. The plates motions are characterized by varying velocities, this variance results to sub sequential collision of two plates (leading to formation of a mountain in a convergent boundary), drift of two plates (leading to formation of rifts in a divergent boundary), or parallel movement in a transform boundary(Webcache 3).