Cenozoic basement structure of the South China Sea and adjacent areas by modeling and interpreting gravity data

Dung, Tran Tuan; Que, Bui Cong; Phuong, Nguyen Hong

doi:10.1134/s1819714013040088

Cited by 13 publications

(3 citation statements)

References 2 publications

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“…8f). We believe that the green polylines are a new boundary because it wasn't shown in the projects and articles [9,14]. This boundary is only detected base on our algorithm by the bouguer gravity anomaly.…”

Section: Real Data Applicationmentioning

confidence: 92%

A Gauss Elimination Method for estimating locations of extrema in gridded data: Applications for Potential Field Data

Kim

Tuan

2020

Preprint

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Abstract. Extrema in gravity measurements can be used to locate geological structures of interest and the boundaries of such structures can be associated with the maxima in the gradients of the gravitational field strength. Finding the extrema of measured geophysical fields measured on the Earth's surface when the data is sparse is challenging. The inferred positions of such extrema are highly model dependent. Polynomial functions of two variables can be fitted to the data. Higher order polynomials typically give more accurate determination of the extrema, but the maximum order of the polynomial is limited by the number of data points. Difficulties are accentuated in the vicinity of boundaries of the existing data. The maximum horizontal gradient method has often been applied in this context. But in that particular construction, quadratic functions are developed in each dimension. Although the magnitudes of the extracted coefficients are obtained from three points related by their positions on orthogonal straight lines, off axis information should be included as well. The present paper introduces a modification of the maximum horizontal gradient method to overcome these difficulties. A Function f of the two variables x and y: f(x,y) = a1x2 + a2y2 + a3x2y2 + a4x2y + a5xy2 + a6xy + a7x + a8y + a9 is established by Gaussian elimination method base on a 3x3 neighborhood data grid. An extract creates a 4-dimensional space based on 4 specific cases of function f, including x = 0, y = 0, y = −x and y = x, they are four functions of one variable. The extreme points position are detected from these functions of one variable. To prove the proposed theoretical basis, as well as the built computer program, the paper presents two numerical models. The obtained results shown that the new approach has more maxima points than the traditional approach. Beside advantages of new approach, some disadvantages is also discussed in this paper. Moreover, we conclude with the application of our new approach to gravitational data in the East Vietnam Sea and demonstrate that we thereby disclose the existence of a gravity trench undetectable in the traditional method.

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Section: Real Data Applicationmentioning

confidence: 92%

A Gauss Elimination Method for estimating locations of extrema in gridded data: Applications for Potential Field Data

Kim

Tuan

2020

Preprint

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“…This boundary is introduced as a spreading axis or spreading ridges of the South China Sea (or the East Vietnam Sea), but isn't described detail (Zhao al., 2020;Wang et al, 2020;Zhang et al, 2018;Ding et al, 2018;Pubellier et al, 2017;Claude et al, 2016). In some paper, this boundary isn't described (Dung et al, 2013;Hiep N., 2005) and, consequently, it reveals a new result for the study area. In order to verify the new boundary and obtain information about its nature, more geophysical and geological works should be carried out.…”

Section: Real Data Applicationmentioning

confidence: 96%

Estimating the Extreme Values in Gridding Data using Gauss Elimination Method: A New Approach in Potential Field Processing

Dung

Gómez-Ortíz

Abdulrazzaq³

et al. 2021

IGJ

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The position of a maximum point of a function depends on its coefficients and order. The maximum horizontal gradient method is a popular method that greatly contributes to the detection of maximum points and approximation of geological structures edges. By adopting a mathematical logic, Blakely and Simpson established a quadratic function based on the characteristic of three points of a straight line in the fundamental directions. However, for potential field data like gravity and magnetic data, the coefficients of a quadratic function in each direction are not only dependent on the values of three points on a straight line, but also, they depend on the values of the surrounding points. This article proposes an algorithm which can detect maximum points more effectively in order to delineate geological structures boundaries from potential field data. The proposed algorithm uses a 3×3 neighborhood data grid to establish a two-variables function and to determine its coefficients by applying the Gaussian elimination method. After the two-variables function has been established, the algorithm estimates any extreme points and their positions from a set of four single-variable functions which correspond to the horizontal, vertical and the two diagonal directions by the cases x = 0, y = 0, y = -x and y = x of the main function. Finally, the conditions to detect the maximum point from the extreme points are defined. The validity of the algorithm was demonstrated on synthetic datasets generated by two different model structures. A real data application of the method has also been realized by estimating the geological boundaries by gravity data in the Vietnam’s continental shelf. The results obtained from the synthetic applications of the algorithm proved that it can determine more maximum points as compared to Blakely and Simpson method, and as a result, in all the test cases, it has drawn the real boundaries of the model structures more accurately. The application results of the method on real data revealed new boundary delineations in the research area, interpreted to be faults or fractures which lies between deep trench in the East Vietnam Sea.

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“…Tác giả cũng sử dụng phương pháp gradient ngang để xác định vị trí và hướng đổ của các đứt gãy trong đới kinh tuyến 109 o với giả thiết là vị trí đứt gãy trùng với các dải vectơ gradient cực đại kéo dài và có cùng phương và quy mô của các đứt gãy được ước lượng từ các dị thường trọng lực ở các mức nâng trường (hay tần số) khác nhau. Ở những phạm vi khác nhau và tại những phân đoạn khác nhau, vị trí và các đặc trưng hình học của đới đứt gãy kinh tuyến 109 o cũng được một số tác giả khác xác định trên cơ sở phân tích các tài liệu trọng lực, từ và địa chấn thăm dò[5,10]. Các kết quả nghiên cứu đều đi đến sự thống nhất là đới đứt gãy kinh tuyến 109 0 là một hệ thống đứt gãy cắm sâu xuyên qua vỏ Trái đất vào tầng Thượng Manti, với góc cắm khoảng 60-80 o .…”

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Scenario-based tsunami hazard assessment for the coast of Vietnam from the \(109^{o}\) Meridian fault zone

Hong

Cong

Van

et al. 2022

VJMST

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Located on the continental shelf and stretching approximately 1,000 km along the Central and Southern Central coasts of Vietnam, the 109o Meridian Fault system has long been recognized as seismically active. Empirical evidence of the seismic, volcanic, and submarine landslide activities also suggests that this fault might be capable of originating near-field tsunamis, which can harm the Vietnamese coastal zone. This paper investigates the possibility of the near-field tsunamis from the 109o Meridian Fault and their impact on the Vietnamese coasts. Location and segmentation of the 109o Meridian fault were determined using seismological, geophysical data, and geomorphologic evidence. The fault’s seismotectonic and geodynamic characteristics were used to model the tsunami source. The COMCOT model was used for simulating three worst-case tsunami scenarios excited by earthquakes with Mw = 8.0 originated in two different segments of the 109o Meridian Fault source. The relationship between tsunami wave height and the source-to-coast travel time is investigated in detail at the virtual sea-level stations distributed along the Vietnamese coastline. The simulation results are presented in the deep-ocean tsunami amplitude maps for the entire East Vietnam Sea region and the coastal tsunami amplitude maps for the Vietnamese coasts. The simulation results show the highest tsunami hazards concentrated along the Central and Southern Central Vietnam coastal zones (from Quang Nam province to Ba Ria-Vung Tau province), with the highest tsunami waves not exceeding 4 m observed off-shore the Quang Ngai, Phu Yen and Ninh Thuan provinces. The shortest tsunami travel time from the source to the Southern Central coast is 35 minutes. Due to its strike-slip mechanism, there is a low possibility of the 109o Meridian fault generating earthquake-triggered tsunamis. Moreover, even if they occurred, the near-field tsunamis generated from the 109o Meridian fault source can hardly cause severe damage and losses for the coastal zones of Vietnam, as shown by the simulation results. Nevertheless, the worst-case scenarios simulation results provide the highest risk that the near-field tsunamis from the 109o Meridian fault source might affect the Vietnamese coasts, which is helpful for the national tsunami warning and response purpose.

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Cenozoic basement structure of the South China Sea and adjacent areas by modeling and interpreting gravity data

Cited by 13 publications

References 2 publications

A Gauss Elimination Method for estimating locations of extrema in gridded data: Applications for Potential Field Data

A Gauss Elimination Method for estimating locations of extrema in gridded data: Applications for Potential Field Data

Estimating the Extreme Values in Gridding Data using Gauss Elimination Method: A New Approach in Potential Field Processing

Scenario-based tsunami hazard assessment for the coast of Vietnam from the \(109^{o}\) Meridian fault zone

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