E. Asakawa

JGI, Inc.

A new method to estimate both subsurface structure and velocity diswibution using seismic trevaeltimes is proposed. Reflection tomography is often used to estimate subsurface velocity distribution and it requires an initial estimate of the positions of reflectors because ray-tracing has to be performed before tomographic inversion. Most conventiona...

We are planning to conduct the multi-component ocean bottom cable (hereafter OBC) seismic survey to monitor the methane hydrate dissociation zone at the 1st offshore methane hydrate production test site in the eastern Nankai Trough, Japan, in 2013. We conducted the first OBC survey in the methane hydrate concentrated zone around the eastern Nankai...

High-resolution images are required for the exploration of mineral resources on and beneath the deep seafloor. Under the Strategic Innovation Promotion Program launched by the Council for Science, Technology, and Innovation in Japan, we developed a survey system using a deep-towed acoustic source and receivers that produces very high-resolution sub...

Concentrated metals such as seafloor hydrothermal deposits and rare earth rich mud are expected to be used as marine mineral resources. Understanding subseafloor structures by the seismic reflection survey is necessary to understand the spatial distribution of marine mineral resources. The imaging accuracy of the subseafloor structure depends on th...

We have developed deeply-towed mechanical driven marine seismic vibrator (MSV) for the use in time-lapse seismic reflection survey to monitor offshore hydrocarbon reservoirs, in which interstitial fluids move with the production, for the optimization of recovery. For this objective, we evaluate the survey performance using MSV and revisited the dat...

We propose a new processing approach not only to correct but to exploit the effects of the motion of marine vibratory source deployed an offshore seismic survey. We decompose the survey data into plural sections as a function of time, space and signal frequency. The instantaneous spatial locations of shot/receivers as a function of time and signal...

The deep-towed Autonomous Cable Seismic (ACS) system is a high-resolution acoustic survey system designed for use in deep-water environments. This system uses a high-frequency acoustic source and a multichannel receiver cable. A common problem in the analysis of deep-towed ACS data is the unstable positioning of the source and receivers due to ocea...

Marine mineral resources such as seafloor hydrothermal deposits, cobalt-rich crusts and manganese nodules have been discovered around Japan. The authors have developed new survey tools for exploration of deep-sea mineral resources and examined the efficiency of the survey system. In 2018, an integrated survey including core sampling was conducted i...

Gas hydrates are located in the permafrost and in deep water shallow sediments, where low temperature and high pressure satisfy the stability conditions of methane clathrates to remain as solid compounds. Hydrates are found in a form of fine layered or altered layered structure with hiatuses and necessitate high resolution surveys, which may not be...

We conducted a marine seismic reflection survey using both an airgun array and a marine seismic vibrator (MSV) designed to be towed in water. The maximum power of seismic emission of the airgun array was about 40 dB larger than that of the MSV. The same survey line was traced twice for comparing the performance of the two different seismic sources....

We propose an innovative approach to achieve the high signal to noise ratio(SNR) of offshore seismic survey data and to reduce the environmental impact in the offshore, deploying a marine seismic vibrator (MSV) as an artificial active source. The combination of interferometric approach for both source and receiver locations could increase the numbe...

In SIP project “Next-generation technology for ocean resources exploration”, we have been developing “Integrated Survey System” for concealed SMS exploration. In this approach, seismic survey is one of key technologies to investigate subsurface structure with high resolution. The Multi-Stage Seismic Survey is our proposed reflection seismic methods...

2) J-MARES/NSENGI, (3) J-MARES/MMTEC, (4) J-MARES/JAPEX In 2014, the Strategic Innovation Promotion Program (SIP) was launched by "the Council for Science, Technology, and Innovation (CSTI)" in Japan. It is an interdisciplinary program among government, academy and industry. It addresses eleven issues selected by consideration of the critical socia...

We propose a novel approach to realize the practical offshore shear wave exploration without any contact of seismic source to seafloor by employing a marine vibratory source and interferometric approach. We conducted scaled experiments and a sea trial, and confirmed that the dipole sound source could enhance the reflected shear waves from the subsu...

Marine wide-angle seismic data obtained using airguns and ocean bottom seismographs (OBS) are effective for determining large-scale subseafloor seismic velocities, but they are ineffective for imaging details of shallow seismic reflection structures because of poor illumination. Surface-related multiple reflections offer the potential to enlarge th...

We developed a towed marine seismic vibrator (MSV) as a new type marine seismic source that employed the hydraulic servo system for the controllability both in phase and in amplitude of the signal being emitted. MSV could mitigate a risk of the impact to the marine environment while satisfying the necessary condition of seismic sources and could en...

This paper demonstrates that the generalized effective-medium theory of induced polarization (GEMTIP) can properly represent the induced polarization (IP) phenomenon in the rock samples collected from submarine hydrothermal deposit. The QEMSCAN mineralogical analysis is deployed in order to clarify the contents of minerals in the rock samples. The...

The Cabinet Office, Government Japan started the Cross-ministerial Strategic Innovation Promotion Program (SIP) in which “Next-generation technology for ocean resources exploration” is scheduled from 2014 to 2018. J-MARES (Research and Development Partnership for Next Generation Technology of Marine Resources Survey) is a private partnership partic...

Vertical cable seismic (VCS) system has been developed to provide higher resolution structure under the seafloor than conventional surface seismic reflection survey. We have applied the VCS to delineate the Seafloor Massive Sulfides (SMS) which has complex structure since 2009. According to past surveys around SMS area, we have already demonstrated...

Full waveform inversion requires a good initial model in order to converge to the correct solution. Most of the methods which develop initial velocity model either require times or additional source of data, e.g. travel time tomography, migration velocity analysis, or horizon guided well log interpolation. We believe the velocity models which are c...

Vertical Cable Seismic (VCS) is a reflection seismic survey method, which uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by seismic sources. It is useful for obtaining a high fidelity image over shallow, narrowly bounded areas, such as potential hydrothermal deposits. However, the irregular geometry in...

In the Seafloor Massive Sulfide (SMS) exploration, the buried sulfide deposits without hydrothermal activity are important for mining development. We had proposed Vertical Cable Seismic (VCS) for exploration of SMS and found out it could reveal the buried deposit through surveys. The conventional VCS data processing gave us the large-scale 3D struc...

We developed a towed marine seismic vibrator (MSV) as a new type marine seismic source that employed the hydraulic servo system for the controllability both in phase and in amplitude of the signal being emitted. MSV could mitigate a risk of the impact to the marine environment while satisfying the necessary condition of seismic sources and could en...

Within the EEZ of Japan, numerous surveys exploring ocean floor resources have been conducted. The exploration targets have been gas hydrates, mineral resources (manganese cobalt rich crust or rare earth) and especially seafloor massive sulphide (SMS) deposits. These resources exist in shallow subsurface areas in deep waters (>1000m). For seismic e...

For the estimation of the hydrothermal mineral deposits reserves, geophysical exploration is indispensable, and the practical geophysical survey was conducted in 2013 at the Izena cauldron in the Okinawa trough, known distribution area of the hydrothermal deposits. Shallow seismic data were successfully acquired by the Vertical Cable Seismic method...

In this paper we examine the application of Equivalent Offset Migration (EOM) to Vertical Cable Seismic (VCS) survey data to extract the subsurface velocity model. We present our method of applying EOM to VCS data and the results from processing two survey datasets. We find EOM to be a useful tool in extracting the velocity model from VCS data. The...

Full Waveform Inversion (FWI) of seismic data is a high resolution subsurface imaging tool and there is a lot of effort to fully industrialize it. The method, which uses a gradient based data fitting approach to minimize the misfit between observed and simulated waveforms, strongly requires either a good initial model or low frequency data for the...

Initializing the Full Waveform Inversion (FWI) iterations from sufficiently low frequencies through a multiscale scheme provides long wavelength information in the early stages of FWI and yields the convergence to the correct solution of the problem. However, because of the band-limited nature of the acquired seismic data the low frequency componen...

Full waveform inversion (FWI) of seismic reflection data has been widely used with different 2D/3D data acquisiton geometries. The method develops a reliable subsurface model by minimizing misfit between observed and simulated waveforms. Vertical Cable Seismic (VCS) is a recent seismic reflection method which uses vertical array of hytdrophones in...

We have fabricated an underwater vibratory seismic source with the scale of 60-70 %, to the real design for towed marine seismic vibrator (MSV) using hydraulic servo system. Several evaluation tests were conducted in the sea using the downsized MSV at a depth of about 250m in water. The performance of the downsized MSV was tested for maximum sound...

In 2014, Japanese Government starts " Next-generation technology for ocean resources exploration " program, one of the issues of " Cross-Ministerial Strategic Innovation Promotion Program (SIP) " to accelerate these research and development of sensing technology, sampling technology, development of the method of environmental impact assessment, and...

The Vertical Cable Seismic (VCS) survey is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by seismic sources. Because the VCS is an efficient high-resolution 3D seismic survey method for a spatially bounded area, we proposed it for the SMS survey tool developme...

The Vertical Cable Seismic (VCS) is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by sea surface, deep-towed or ocean bottom sources. This method is useful to delineate detailed structures in a spatially-limited area below seabed in the deep sea where conventi...

The VCS survey is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by seismic sources. Because the VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed it for the SMS survey tool development program started by Jap...

Full waveform inversion (FWI) produces subsurface images by minimizing the misfit between observed data and calculated model using iterative local optimization algorithms like conjugate gradient method. This approach requires a starting model which should appear in the neighborhood of the global solution of the FWI problem to ensure that the modele...

Water temperature, salinity concentration, current velocity distribution, etc. in the ocean, are very important physical properties to understand the thermal structure of the ocean. The monitoring of these physical properties could be achieved by either of two kinds of measurement schemes, i.e., one the direct measurements using instruments such as...

Surface based microseismic monitoring during hydraulic fracture stimulations is an emerging technology in the last decade. The method observes acoustic emission (AE) or microseismic events using a surface receiver array and estimates source locations and origin times of the events by analyzing a time series of migration images from observation data...

ater temperature, salinity concentration, current velocity distribution, etc. in the ocean, are very important physical properties to understand the thermal structure of the ocean. The monitoring of these physical properties could be achieved by either of two kinds of measurement schemes, i.e., one the direct measurements using instruments such as...

We applied the seismic interferometry to marine wide-angle data in order to obtain a deep crustal reflection profile without spatial imaging gaps due to sparse deployment of ocean bottom seismographs (OBSs). While the airgun-OBS wide-angle survey is useful to acquire reflections or refractions from deep crustal structures, it is difficult to obtain...

Figure 1. PSDM images in the fore-arc region of the Izu-Bonin Island Arc using MCS data (a), using OBS data (b), and using SI data (c) (Sato et al., 2012). Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (tsato@jamstec.go.jp), ABSTRACT P re-stack depth migration (PSDM) is one of the effective methods to clarify the detailed crustal s...

This study investigates the effectiveness and the applicability of full waveform inversion (FWI) method to estimate underwater sound velocity structures. We use a frequency domain full waveform inversion method in this study. We use an adjoint-state method for the calculation of the gradient in an iterative inversion based on a pre- conditioned con...

The first offshore methane hydrate production test will be conducted by METI and JOGMEC/MH21 in early 2013 in the eastern Nankai Trough, Japan. The test aims to prove the applicability of the depressurization technique for MH production. The flow test intervals will be at shallow sediment depths but at deep water depths. JOGMEC plans to carry out a...

We developed a new OBC (Ocean Bottom Cable), named as 'DSS' (Deep-sea Seismic System). The sensor has 3-component accelerometer and a hydrophone applicable for four-component (4C) seismic survey. Using the DSS, the methane hydrate dissociation zone will be tried to be monitored at the water depth of around 1000m during JOGMEC offshore methane hydra...

A demand for laying an observation cable system on a planned route position precisely has become higher and higher. JOGMEC, JGI, OCC and KCS carried out a methane hydrate dissociation monitoring survey under the seabed by using DSS (Deep-sea Seismic System) last year. The laying position of the seismometer located in the central of the DSS was requ...

The vertical cable seismic is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. Because the VCS is an efficient high-resolut...

The vertical cable seismic is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. This type of survey is generally called VCS...

A 2D multi-component seismic survey was carried out in the Nankai Trough using the RSCS (Real-time Seismic Cable System) in FY2006. The RSCS is the newly developed ocean bottom cable system which is usable in more than 2000m water depth. The results of the PP and PS components gave us much information of the methan hydrate bearing zone. Based on RS...

The active source seismic surveys are generally divided into two major types; one is the near-vertical seismic reflection survey (e.g. Multi-Channel Seismic reflection survey) and the other is the wide-angle seismic reflection and refraction survey (e.g. airgun-OBS survey). The near-vertical reflection survey is characterized by densely spaced shot...

In 2009, Ministry of Education, Culture, Sports, Science and Technology(MEXT) started the survey system development for Hydrothermal deposit. We proposed the Vertical Cable Seismic (VCS), the reflection seismic survey with vertical cable above seabottom. VCS has the following advantages for hydrothermal deposit survey. (1) VCS is an efficient high-...

A 2D multi-component seismic survey was carried out in the Nankai Trough using the RSCS (Real-time Seismic Cable System) system in 2006. The RSCS is the newly developed ocean bottom cable system which is usable in more than 2000m water depth. The results of the PP and data PS components gave us much information of the methane hydrates bearing zone....

The vertical cable seismic is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. This type of survey is generally called VCS...

In 2009, Ministry of Education, Culture, Sports, Science and Technology(MEXT) started the survey system development for Hydrothermal deposit. We proposed the Vertical Cable Seismic (VCS), the reflection seismic survey with vertical cable above seabottom. VCS has the following advantages for hydrothermal deposit survey. . (1) VCS is an effective hig...

High frequency seismic reflection surveys using deep-towed streamers are now of interest to explore sub-seafloor structures bearing hydrothermal deposit with adequate resolution. One of the problems arose with the utilization of the deep-towed streamer is the navigation or the location estimation of seismic sources and streamers to assure the neces...

Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Potential new deposits of lead-zinc-copper sulfide are generated by cooling hot water around the vents. There are about ten hydrothermal deposits founded around the water depth of 1000m along Izu-Ogasawara...

In the methane hydrate research project by METI/MH21 consortium, some unconventional data analysis techniques are developed and various types of geophysical surveys have been carried out to estimate the distribution and characteristics of methane hydrate. In this paper, we describe the continuous velocity analysis technique, 2D multi-component seis...

The estimation of crustal structure is a key to reveal the tectonic history of the Japanese island arc and to study the future tectonic activity, such as earthquakes, volcanic eruptions, or associated tsunamis. Refraction or reflection wave exploration is one of the methods for deep oceanic crust investigation, but in these methods mainly used is o...

The METI Sado-oki Nansei 3D seismic survey was carried out in deep water southwest off Sado Island, Japan Sea. The survey area covered the Umitaka Spur, which features mounds and pockmarks according it's central ridge. Other surveys sampled large masses of methane hydrate beneath the sea floor, discovered methane bubble plumes rising into the water...

A high frequency deep-tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data. A special feature of the survey is that both the source and t...

In this study, we present two types of simulation models that consist of a sediment layer, a crust layer, and a sloped interface that are marked as seismic velocity discontinuities. Seismometers are aligned on the seafloor. One model has only surface seismic sources and the other has buried seismic sources that are equivalent to natural earthquakes...

A high frequency deep-tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data. A special feature of the survey is that both the source and t...

We have developed the Decomposed element-free Galerkin method (DEFGM), a kind of three-dimensional finite-element method for solving wave-propagation problems. We first compared the DEFGM with analytical or reflectivity method for checking the accuracy. The DEFGM produced very accurate resolutions. We second conducted the simulation comprising both...

doi:10.1190/1.3255424

Receiver function analysis is known as a method frequently practiced to utilize both vertical and horizontal components of seismic records to reveal subsurface structure using earthquake signals in natural seismology. In the receiver function analysis, a receiver function is estimated by the deconvolution of P-SV horizontal record with the vertical...

Various types of geophysical surveys other than conventional 2D/3D marine seismic have been carried out for the purposes of estimating the distribution and characteristics of methane hydrate. They are a 2D deep- towed seismic survey, OBS surveys and a 2D multi-component survey with ocean bottom cable. We summarize these surveys and results. A 2D de...

A high frequency deep-tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data in the area. A special feature of the survey is that both the...

Export Date: 27 June 2012, Source: Scopus, Language of Original Document: English, Correspondence Address: Asakawa, E.; JGI, Inc., References: Asakawa, E., Mizohata, S., Kasahara, J., Nishizawa, A., Ocean Bottom Imaging using Multiple Reflected Water Waves Obtained by OBS (2007) European Geosciences Union General Assembly, 2007, pp. A0337;

We propose a newly-developed depth imaging approach for OBS (Ocean Bottom Seismometer) reflection data in active-source structural surveys using wavefield separation and PSDM (Prestack Depth Migration). OBS data includes a lot of valuable signals, not only reflection but refraction. However its wavefield is contaminated with various kinds of waves...

RSCS (Real-time seismic Cable System) is a new real-time seafloor reflection seismic observation system. It is a series of 3-component geophones and telemetry opto-electronics equipped into a high pressure resistant housing, which enables real-time seismic data acquisition at ultra deep sea. The first reflection seismic survey was carried out in Ma...

We propose a newly-developed depth imaging approach for OBS (Ocean Bottom Seismometer) reflection data in active-source structural survey using wavefield separation and PSDM (Prestack Depth Migration). OBS data includes a lot of valuable signals not only reflection but refraction. However its wavefield is contaminated with a various kind of waves t...

The RSCS (Real-time Seismic Cable System) is an optical submarine cable system employing a series of 3 axial component velocity type sensors (geophones) mounted in a pressure resistant case capable of withstanding hydraulic pressures up to 800 atmospheres (78.4 MPa). Spreads consisting of several of geophones, spaced at 50 meters interval, have bee...

To detect the change of physical properties in small areas, a se-ries of high-resolution waveform inversions is applied to time-lapse seismic data. A procedure by use of differentiation be-tween the time-lapse data and normalization using reference data is proposed in this study. The procedure is derived as a straight-forward extension of waveform...

As one of approach to evaluating the total amount of methane hydrate, a method utilizing the results of velocity analysis on reflection seismic exploration data is studied. Well log sonic data reveals that the velocity of the methane hydrate bearing zone is greater than that of surrounding sediments. Thus, the velocity information can be used for d...

A 2D deep-towed seismic survey was carried out over part of the Nankai Trough, Offshore Japan, in 1996. The area is known to have a major accumulation of methane hydrate; conventional seismic surveys have mapped thousands of sq. km. of BSR events, and the presence of methane hydrate was confirmed by a MITI research well in 2000. The objective of th...

Many authors have investigated the raytracing methodologies for two-point problems between a source and receiver. Multi-point raytracing of reflected waves, multiples and converted waves is also potentially very important for seismic data processing, but a practical method is not yet widely known. In this paper, a practical approach for the raytrac...

Oil and gas explorations in mountainous regions are becoming more important to find unexplored possible reserves. Here, the seismic survey technique is a major exploration tool as well. However, difficulties often come from complicated topography change. For evaluating the topographic effects, we conducted the feasibility study for a 2D seismic sur...