R/V Natsushima Cruise Report NT Title of the cruise. Boso Peninsula and development of in situ calibration for. DONET pressure gauge

Transcription

1 R/V Natsushima Cruise Report NT15-12 Title of the cruise Deploy and retrieval of ocean bottom instruments at off Boso Peninsula and development of in situ calibration for DONET pressure gauge July15,2015-July 24,2015 Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

2 Contents 1. Cruise Information 2. Researchers 3. Observations 4. Notice on Using

3 1. Cruise Information Cruise ID: NT15-12 Name of vessel: R/V Natsushima Title of the cruise: Deploy and retrieval of ocean bottom instruments at off Boso Peninsula and development of in situ calibration for DONET pressure gauge Title of proposal: Theme1: Observation of slow slip events off the Boso Peninsula using ocean bottom tiltmeter and ocean bottom pressure gauges Theme2: Development of in situ calibration for pressure gauges using mobile pressure gauge Cruise period: 15-24, July, 2015 Ports of departure / call / arrival: Yokosuka - Kumamoto Research area: off Boso Peninsula, Kumano-nada Research Map Fig. 1.1 Research Area in off Boso and ship track (thema 1).

4 D km C0002G Fig. 1.2 Research Area in Kumano-Nada (theme2)

5 2. Researchers Chief scientist: Toshinori Sato [Graduate School of Science, Chiba University] Representative of the science party: Toshinori Sato [Graduate School of Science, Chiba University] Shuhei Nishida [JAMSTEC] Science party (List) <Theme 1 Group> Toshinori Sato, Chiba Univ. Hajime Shiobara, ERI, Unv. Tokyo Tateo Yagi, ERI, Univ. Tokyo Akihiro Kono, Chiba Univ. Asami Terada, Chiba Univ. Taiyu Mori, Chiba Univ. <Theme2 Group> Shuhei Nishida, JAMSTEC Yuya Machida, JAMSTEC Captain, crew and Hyper Dolphin operation team (List) R/V NATSUSHIMA Officers and Crew Captain MASUJIMA HIROAKI Chief Officer CHIBA MASATO 2nd Officer KONNO HIDEHIKO 3rd Officer YOSHIDA SATORU Chief Engineer KAJINISHI KIYONORI 1st Engineer MATSUKAWA KIMIO 2nd Engineer SHIRAKATA KENICHI 3rd Engineer ONO KAZUKI Chief Electronics Operator SAITAKE HIROYASU 2nd Electronics Operator ISHIWATA HIROKI 3rd Electronics Operator TAKAKUWA TATSUHIRO Boat Swain ODA HATSUO Able Seaman YAMAMOTO SHUICHI Able Seaman NAGAI HIROAKI Able Seaman ABE SHUN Able Seaman NAKANISHI TORU Sailor KOJIMA SHINYA Sailor SAGA TOSHIYA No.1 Oiler OISHI HIROYUKI

6 Oiler Oiler Oiler Oiler Oiler Chief Steward Steward Steward Steward Steward Steward Hyper Dolphin Team Operation Manager 1st ROV Operator 2nd ROV Operator 2nd ROV Operator 2nd ROV Operator 2nd ROV Operator 3rd ROV Operator 3rd ROV Operator Marine Technician Nippon Marine Enterprises, LTD. FUJIWARA MASAYUKI TANAKA MASAKI WATANABE TAKUYA HIDAKA TORU NAKAJIMA KOSHI SASAKI SUETO TANAKA SHINSUKE FUKUMURA HIDEO SUZUKI AKIO MIKAMI SOTA KASHIWAGI KOICHIRO KONDO TOMOE WAKAMATSU HOMARE CHIBA KATSUSHI KIDO TEPPEI SAIGO RYO IHARA SHOTA GOTO TAKUMA KUMAGAI SHINNOSUKE TAKUYA ONODERA

7 3. Observations 3.1 Observation of slow slip events off the Boso Peninsula using ocean bottom tiltmeter and ocean bottom pressure gauges Objectives This survey was conducted for IODP proposal, the Kanto Asperity Project (KAP) program B. KAP Program B is a long-term monitoring project for observing several cycles of slow-slip events (SSEs) to reveal slow-slip phenomena and to improve earthquake generation models. The discovery of SSEs has added a major new factor to our understanding of how plate boundaries accommodate relative plate motions. Plate boundaries were previously thought to relieve stress through either continuous aseismic sliding or earthquakes with instantaneous failure. SSEs are an important global mechanism regulating stresses on plate boundaries, and a key to a full understanding of tectonic behavior at plate boundaries. To investigate SSEs, many studies have applied earthquake generation models, usually used for typical earthquakes, to SSEs. Although these simulation studies are useful for understanding the processes of SSEs, earthquake generation models are not yet fully successful. Among the issues to be addressed, two are especially important: (1) previous models were developed using data from laboratory experiments rather than natural events, and (2) previous models have used several different fault constitutive laws. Continued progress in earthquake generation models requires data from long-term observations over entire event cycles, with which simulations using several fault constitutive laws can be conducted. This project proposes to improve earthquake generation models and better understand the processes of SSEs based on data from SSE monitoring and simulations. For these observations and simulations, the Boso SSEs are one of the best candidates because they occur every 2 7 years, allowing us to obtain data on two or three whole event cycles during years of observation. Unlike most studies of geologic processes, KAP Program B holds the promise of quickly achieving model improvements by repeated forecasting and observation of SSEs, allowing feedback from observations to the model. Therefore, establishing earthquake generation models using data from SSEs holds out the promise of a great and rapid advance in earthquake science. This project proposes drilling at six offshore sites and constructing an observation network covering the Boso SSEs to record the slip distribution during entire SSE cycles. Measurements will be made with highly sensitive tiltmeters, broadband seismometers, and depth sensors installed in boreholes. To conduct this project, we need to detect precise slip area of the SSE. So, we conduct long-term pressure observations using ocean bottom prresure gauges to obtain vertical deformation due to the Boso SSE. This survey conducts deployments and retrievals of these instruments. Adding the six offshore borehole sites, we need sea floor observations to obtain spatially dense data. So, we started long-term observation of the next generation broadband ocean bottom seismometer with tilt-meter function (BBOBST-NX). Our final aim is to realize the spatially dense tilt observation on the sea floor. This survey conducts deployment of the BBOBST-NX with the ROV Hyper Dolphin. The

8 position of the BBOBST-NX is chosen at the center of large displacement by the Boso slow slip event repeatedly occurred Survey July 18th We retrieved 2 OBP-ERIs and deployed 2 OBP-ERIs at KAP3 and BOSO2. We conducted position researches for both OBPs. After that, bathymetry researches were conducted at KAP2 and KAP3. July 19th We retrieved 1 OBP-ERI and deployed 1 OBP-ERI at BOSO1. At KAP3, we dropped the BBOBST-NX with the ROV homer and conducted research of the landing position. After the landing position was determined, the #1854 dive was started (Fig ). The BBOBST-NX was easily found by using the ROV homer. Unlocking and moving of the recording unit from the sensor unit were finished about half an hour. The tilt of the sensor unit was smaller than the limit for the proper operation. Finally, the view of the instruments was checked as in Fig Then, we searched an ocean bottom seismometer with pressure gauge (OBSP). The HPD found the anchor of the OBSP, but could not found the OBSP itself. After retrieval of the HPD, we deployed 1 OBP-CHU at KAP3 and conducted position research of it.

9 Fig The site location map of the BBOBST-NX and other instruments. Fig View of the BBOBST-NX in observation at the seafloor.

10 Fig Dive Trajectory at KAP3 (dive #1854) Fig OBP-ERI (left) and OBP-CHU (right)

11 3.1.3 Data on deployed instruments Name site latitude longitude depth call BBOBST-NX KAP SI2: 544 OBP-ERI BOSO SI2: 640 OBP-ERI BOSO SI2: 742 OBP-ERI KAP SI2: 694 OBP-CHU KAP Nichiyu: 058

12 3.2: In situ calibration for pressure gauges using a mobile pressure gauge The purpose of the Observation DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) is a submarine cabled real-time sea floor observation network which was designed to realize precise earthquakes and tsunamis monitoring on safer in the long period of time. However, in order to measure the crustal deformation using a crystal water pressure meter with DONET, it is necessary to compensate for the error due to instrumental drift. Therefore, in order to estimate an accuracy of a mobile pressure gauge, we measured a repeatability and hysteresis of the sensor. The purpose of this cruise are (1) to repeat measurement using a mobile pressure sensor near pressure gauge on seafloor, (2) to measure the difference of pressure between two observatories based on a mobile pressure gauge Instruments We were developed a mobile pressure sensor which has two pressure hulls. #1 pressure hull has a recorder, power and external communication boards. #2 pressure hull has pressure sensor (Paroscientific Inc. 410K), electric valve and heater. #3 is pressure sensor (Paroscientific Inc. 8B7000-I-005) in a cylinder. Fig a mobile pressure sensor

13 3.2.3 Dive information Dive Summery DIVE #1855 on July. 21, 2015: A measurement of a precise water pressure using a mobile pressure gauge on the C0002 platform In this dive, an ROV Hyper Dolphin (HPD) was operated for a measurement of a precise water pressure on the C0002 platform using a mobile pressure gauge. First, the HPD landed near the C0002 platform. We opened a valve of the pressure gauge to measure a water pressure on the sea floor. Then we moved the pressure gauge onto the C0002 platform using the HPD, and placed the mobile pressure gauge. We stayed about 5 hours for thermally stable measurement. After the water pressure measurement, we recovered the mobile pressure gauge and closed its valve. Then we left the sea floor. Fig Approach of the HPD to the C0002 platform. Fig A deployment of the pressure gauge on the C0002 platform. Fig The mobile pressure gauge on the C0002 platform. Fig A recovery of the mobile pressure gauge.

14 Dive Trajectory Fig Dive Trajectory at C0002G (dive #1855)

15 3.3 Shipborading log

16 4. Notice on Using Notice on using: Insert the following notice to users regarding the data and samples obtained. This cruise report is a preliminary documentation as of the end of the cruise. This report may not be corrected even if changes on contents (i.e. taxonomic classifications) may be found after its publication. This report may also be changed without notice. Data on this cruise report may be raw or unprocessed. If you are going to use or refer to the data written on this report, please ask the Chief Scientist for latest information. Users of data or results on this cruise report are requested to submit their results to the Data Management Group of JAMSTEC.