DISTRIBUTION OF SUBSURFACE QUATERNARY SEDIMENT IN SOUTH BINTAN ISLAND WATERS AS A POTENTIAL HEAVY MINERAL PLACER OR RARE EARTH ELEMENT DEPOSIT BASED ON SEISMIC INTERPRETATION

Bintan Island is one of the areas traversed by the Southeast Asian granitoid belt which is known to have the potential for heavy mineral placer deposits. Due to the dwindling presence of heavy mineral placer deposits in land areas, it is necessary to look for the potential presence of heavy mineral placer deposits in water areas. Searching for placer heavy mineral deposits accomodation in these waters requires subsurface mapping.The method used in this subsurface mapping is a single channel seismic method with a total of 179 lines in the direction of northeast – southwest and west – east. The results of this seismic recording are then interpreted the boundaries of the seismic facies unit and distributed using the kriging method. Furthermore, the thickness calculates by using the assumption velocity 1600 m/s.Based on the facies unit boundaries that have been interpreted, the quaternary sediments that formed in the study area are divided into 2 types of units, namely: Unit 2 which is estimated to be fluvial – transitional sediment, and Unit 1 which is estimated to be transitional sediment – shallow sea. There is also a difference in thickness patterns in these two units, where unit 2 shows a pattern of sediment thickening that resembles a paleochannel trending northeast – southwest, while unit 1 is relatively uniform.From the results of this study, it can be said that the area that has potential for heavy mineral placer deposits is in the west - center of the southern waters of Bintan Island. Where the potential for heavy mineral placer deposits should be in the paleochannel deposits that are part of Unit 2.

PolarGUI: A MATLAB-Based Tool for Polarization Analysis of the Three-Component Seismic Data Using Different Algorithms

We present an open-source and MATLAB-based tool with an easy-to-use graphical user interface (GUI) consisting of four polarization analysis approaches: the particle-motion trajectory (a hodogram in a 3D plane), eigenvalue decomposition (EVD) based on the covariance matrix (including two calculation methods), singular value decomposition using principal component analysis, and EVD based on a constructed analytic signal matrix (EVD-ASM). We review the calculation processes and features of the four cited methods. The eigenvalue and eigenvector are applied to obtain the polarization attributes of the three-component (3C) seismic data. Using rose graphs and histograms, the corresponding azimuth and incidence angle are calculated to determine the propagation direction of the seismic wave. Statistical distribution curves of the corresponding rectilinearity and planarity of the waves are also plotted. The polarization analysis GUI can simultaneously analyze two selected data sections in a seismic recording corresponding to P and S waves. We evaluate the performance of these algorithms using real 3C earthquake datasets. Comparison tests indicate that the aforementioned four methods have different time consumption, and the differences between the results of the EVD-ASM and those of the other methods are very small.

Measurements of Seismometer Orientation of the First Phase CHINArray and Their Implications on Vector-Recording-Based Seismic Studies

ABSTRACT From 2011 to 2013, the CHINArray project led by the Institute of Geophysics, China Earthquake Administration, made the first phase deployment of 350 broadband seismometers at the southeastern margin of the Tibetan plateau. The three-component records of the CHINArray-I have been widely used in studying seismic structures beneath the margin under the assumption that the two horizontal components of seismometers are well aligned toward geographic north and east. In this study, we estimated the actual orientation of the two horizontal components of the 350 seismometers by analyzing P-wave particle motions of teleseismic earthquakes. Among the 350 stations, we found 80 stations were mildly misaligned by 5°–20°, and another 49 stations had misorientations larger than 20° or other malfunctioning issues. We also investigated how sensor misalignment affects seismic studies that rely on the vectorial nature of seismic recording, such as constructing receiver functions, estimating seismic anisotropy, and extracting surface wave Green’s functions from ambient-noise data. We found a large deviation in sensor orientation could result in wrong results or large measurement errors, whereas a mild sensor misalignment tended to decrease measurement stability and reliability.

Distributed acoustic sensing for seismic monitoring in challenging environments

<p>Our understanding of subsurface processes suffers from a profound observation bias: ground-motion sensors are rare, sparse, clustered on continents and not available where they are most needed. A new seismic recording technology called distributed acoustic sensing (DAS), can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recording over tens of kilometers of linear fiber length. DAS works in high-pressure and high-temperature environments, enabling long-term recordings of seismic signals inside reservoirs, fault zones, near active volcanoes, in deep seas or in highly urbanized areas.</p><p>In this talk, we will introduce this laser-based technology and present three recent cases of study. The first experiment is in the city of Stanford, California, where DAS measurements are used to provide geotechnical information at a scale normally unattainable (i.e., for each building) with traditional geophone instrumentation. In the second study, we will show how downhole DAS passive recordings from the San Andreas Fault Observatory at Depth can be used for seismic velocity estimation. In the third research, we use DAS (in collaboration with Fujitec) to understand the ocean physics and infer seismic properties of the seafloor under a 100 km telecommunication cable.</p>

A new approach for arriving at higher frequencies through stochastic modelling: application to site attenuation (kappa)

<p>We propose a framework for stochastically modelling the Fourier spectrum of the noisy seismic recording, considering that a seismic signal is a random rather than a deterministic quantity. We show that under this assumption, the noisy recording’s periodogram can be modelled as independent Exponential random variables with a frequency-dependent mean. With this model, estimating seismological parameters can be tackled through Maximum Likelihood (ML), allowing a fast, accurate and robust solution. This new approach constitutes a general estimation framework applicable to any parameter estimation that uses spectral analysis. Here we apply it to the high-frequency decay parameter kappa, which is particularly important for estimating and adjusting ground motion on rock. The improved ML performance is shown through a series of experiments on synthetic and recorded seismograms. The biggest advantage of the new method is its ability to account for the noise in the recording instead of just trying to avoid it, as is typically done when any ‘acceptable’ frequency range is isolated through signal-to-noise (SNR) criteria. As a result, our proposed technique can achieve acceptable results even for what would be typically considered very low and often unusable SNR, pushing the boundary of what is considered usable quality in seismic recordings.</p>