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The first stage of field experiments involving the design and construction of a low-power consumption ocean bottom electro-magnetometer (OBEM) has been completed, which can be deployed for more than 180 d on the seafloor with a time drift of less than 0.95 ppm. To improve the performance of the OBEM, we rigorously evaluated each of its units, e.g., the data loggers, acoustic parts, internal wirings, and magnetic and electric sensors, to eliminate unwanted events such as unrecovered or incomplete data. The first offshore deployment of the OBEM together with ocean bottom seismographs (OBSs) was performed in NE Taiwan, where the water depth is approximately 1400 m. The total intensity of the magnetic field (TMF) measured by the OBEM varied in the range of 44 100–44 150 nT, which corresponded to the proton magnetometer measurements. The daily variations in the magnetic field were recorded using the two horizontal components of the OBEM magnetic sensor. We found that the inclinations and magnetic data of the OBEM varied with two observed earthquakes when compared to the OBS data. The potential fields of the OBEM were slightly, but not obviously, affected by the earthquakes. [ABSTRACT FROM AUTHOR]

The first stage of field experiments involving the design and construction of a low-power consumption ocean bottom electro-magnetometer (OBEM) has been completed. To improve the performance of the OBEM, we rigorously evaluated each of its units, e.g., the data loggers, acoustic parts, internal wirings, and magnetic and electric sensors, to eliminate unwanted events such as unrecovered or incomplete data. The evaluations of the procedure included the following. Data logger: digitizer sensitivity, linearity, and errors Acoustic transceiver: "ENABLE," "DISABLE," "RANGE," "RELEASE1," "RELEASE2," and "OPTION1" functions Magnetic sensor: sensitivity of the fluxgate and orthogonality Electrical receiver: potential voltage, impedance, and frequency responses Power consumption: the maximum operating current of two sets of batteries Deployment and recovery procedures on deck We confirmed the optimal performance of the OBEM after repeatedly testing the procedures. The first offshore deployment of the OBEM together with ocean bottom seismographs (OBSs) was performed in NE Taiwan, where the water depth is approximately 1,400 m. The total intensity of the magnetic field (TMF) measured by the OBEM varied in the range of 44,100-44,150 nT, which corresponded to the proton magnetometer measurements. The daily variations of the magnetic field were recorded using the two horizontal components of the OBEM magnetic sensor. We found that the inclinations and magnetic data of the OBEM varied with two observed earthquakes when compared to the OBS data. The potential fields of the OBEM were slightly, but not obviously, affected by the earthquakes. [ABSTRACT FROM AUTHOR]

Taiwan is located in the collision zone between the Eurasia plate and the Philippine Sea plate. The Philippine Sea plate moves to northwest at a rate of 7 cm per year relative to the Eurasian plate resulting in forming a series of fold-and-thrust belts aligned in northeast-southwest direction. Westward compressive forces gave the younger or more active faults are located in the west. Scholars refer the west edge of fold and thrust belts as the location of so-called deformation front. To the north of the Sanyi-Puli Seismic Zone, it is believed the front goes to ocean floor and is located offshore of Miaoli and Hsinchu County.Previous studies indicated that the deformation front follows the trace of Hsinchu fault extending offshore to the place where water depth at 35m. Beneath water layer, sediment strata were deformed compressively to imply its young occurrence. Accordingly, this study was proposed, we therefore believed that the trace of deformation front shall be turned southward and aligned offshore along the coastal line of Chunan-Houlong. The tools to trace the deformation front offshore Chunan and Houlong are reflection seismic system, multi-beam echo sounder and side-scan sonar system in this study. Survey results indicate offshore deformation front appears along a reverse fault with 0.8° dipping angle southeastwards, and its trace extending from Hsinchu Fault to the deeper area over 50 meters depth. There is no evidence showing this outmost trace shall further turn south parallel with the coastal line as it was expected. [ABSTRACT FROM AUTHOR]

Typhoon and earthquake are mainly natural disasters in Taiwan. Accordingly, the dynamic properties of submarine sediments are important issues while there are referring to offshore site investigation, marine structure construction, and resources exploration. The gas hydrate is a potential energy resource and distributed over the continental margin offshore of the south-west (SW) of Taiwan. Because of the requirement of exploration works, lots of marine areas were selected to study their engineering properties of submarine sediments. The geophysical seismic method and geotechnical laboratory tests were performed to establish physical properties and dynamic soil parameters of these selected sites. Data obtained from P-waves and S-waves generated by P–S conversion on reflection from airgun shots recorded along one line of ocean bottom seismometers (OBS) were used to construct 2-D shear wave velocity (Vs) sections. The cores sampled at test sites utilized gravity sampling method and conducted soil laboratory tests. The cored specimens carried out physical property test and the bender element test to obtain physical properties, Vs, and maximum shear modulus (Gmax). Correlations of porosity, Vs, and Gmax were constructed to predict the in situ properties. Results show the prediction equation get approximate values in comparison with the Vs and Gmax measured by field geophysical seismic method. This paper introduces the field and laboratory tests on obtaining dynamic properties, presents all of the test results, and correlate the relationship of dynamic soil properties between field and lab test outputs. [ABSTRACT FROM AUTHOR]