NEAREST 1st Annual Meeting October, Marralech NEARESTWP4 Leader: INGV INGV Team: Laura Beranzoli, Davide Embriaco, Paolo Favali, Francesco Frugoni, Marco Lagalante, Nadia Lo Bue, Giuditta Marinaro, Stephen Monna, Claudio Viezzoli

Summary General on WP4 and WP Tasks Status of the activity Mission details Present status of the experiment

Objectives The WP is aimed at carrying out geophysical and oceanographic measurements on the seafloor and in the water column in the nearby of near-shore tsunamigenic sources for the identifications of tsunami signals. The seafloor and water column measurements will be performed by means of a deep seafloor multiparameter observatory of GEOSTAR type, developed in previous EC projects and will be transmitted to shore in real-time (some essential parameters). WP4 - Tsunami signal detection General

Task 4.1 Definition of sensor requirements and sensor selection; requirements of the detection software (e.g., detection algorithm, triggering threshold, messages). Task 4.2 Design and development of modifications (e.g., sensor supports of the frame); design and development of the software. Task 4.3 Integration of new sensors/devices and new software in the seafloor observatory, tests of the functionality in laboratory. Task 4.4 Preparation planning and implementation of a long-term (about 1 year) mission; cruises for deployment and recovery. Task 4.5 Data back-up, quality checks, preparation of the data base to be integrated with other data; pre-analysis of ‘parent’ tsunami signals. General

ISMAR-BO. FFCUL, CSIC  marine site selection and characterisation for the pilot experimenton the basis of the knowledge of the area ISMAR-BO  cruises responsible AWI, UGR, IM  requirements of sensor sampling rates TFH  MODUS for the pilot experiment (deployment/recovery) INGV  Seafloor observatory (GEOSTAR) ISMAR BO FFCULCSICAWIUBOINGVTFHUGRIMCNRSTXISTOS H H M M Leader H H M Partners involved WP4 General

D10definition of sensors’, software requirements for the deep-sea platform D11detailed design for the integration of new sensors and device in the deep-sea platform D12integration of new sensors, test of functionality of the deep-sea platform D13deployment procedure for the deep-sea platform D14deployment cruise of the deep-sea platform and cruise report D15a recovery cruise of the deep-sea platform and data quality checks D15bcruise report WP4 Deliverables m 4 m 8 m 11 m 12 m 24 General

Experiment overview Acoustic transmission Satellite Link GEOSTAR MODUS Task 4.1 Buoy

GEOSTAR Task 4.1 Tasks: Scientific multiparametric data acquisition on relevant seismic source site Nearly real time warning event (seismic and sea level) identification and notification The GEOSTAR seafloor observatory will be equipped with sensor packages acquisition, control units data processing unit local memory storage acoustic communication system (towards sea surface buoy)

Sensor requirements Sensor rateAcquisition Triaxial broad band seismometer 100Hz - 3 comp. Continuous + (decimated) triggered events Triaxial accelerometer100Hz - 3 comp. Continuous + (decimated) triggered events Hydrophone100Hz Continuous Pressure sensor15sec Continuous Structure accelerometer+Gyros 100Hz - 6 comp. Only on triggered events Gravity meter1Hz Continuous CTD + Transmissometer 1smp/hour Continuous ADCP1profile/hour (40 layers/3 comp.) Continuous Currentmeter5Hz Continuous Task 4.1

Sensors SensorrateMODEL Triaxial broad band seismometer 100Hz Guralp CMG-40 Triaxial accelerometer100Hz Guralp CMG5-T Hydrophone100Hz OAS E-2PD Pressure sensor15sec Paroscientific 8CB Accelerometer+Gyros (IMU)100Hz Gladiator Technologies Landmark 10 Gravity meter1Hz IFSI (INAF) Prototype #2 CTD + Transmissometer1smp/hour SeaBird SBE 16 plus Wet Labs ECO-BBRTD 6000m ADCP1profile/hour RDI Workhorse 300 Khz Currentmeter5Hz Nobska MAVS-3 Task 4.2

Tsunami Detection Procedure Trigger on Pressure and Seismic events Seismometer: trigger on local strong seismic event Pressure: detection of sea level anomalies (Tsunamis wave)  details in the PART 2 of presentation (ISMAR) Task 4.1

Buoy The buoy is equipped with: acoustic communication system (to the seafloor station) satellite communication systems: –to shore stations for data transmission (Globalstar) –buoy position tracking (ARGOS ) meteo station Task 4.1 Tasks: allows communication between GEOSTAR and shore stations (notification of possible tsunamis events) detects meteo data

Hydrophone 3D-ACM corrento metro- da aggiorn are Unique time reference for easy comparison of the signals Paroscientific 8CB Task 4.2 IMU CMG-40T

Buoy layout Task 4.2 Towards GEOSTAR SatelIite

GEOSTAR layout Task 4.2 Towards the surface buoy

Real time Communication scheme Task 4.2 Acoustic link Main station (INGV-Roma) Service station (backUp) Secondary station (ISMAR-BO) Buoy Satellite link LAN - Internet link Auxiliary stations (mailboxes)

Messages/data availables Tipe of messages Available information Direct Recipients PeriodicSea level/meteo data/mission status INGV-ISMAR Event (seismic - pressure) Time of event, pressure data sec) All partners (nearly real time via e- mail) End of mission All sensor dataNEAREST partners Task 4.2

Mission scheduling 10 Aug -5 Sept. r/v Urania (CNR-ISMAR) GEOSTAR deployment in the selected site (B)

Buoy deadweight coordinates: GEOSTAR observatory coordinates: Lat. 36° ’ N Lat. 36° 21,875’ N Lon. 09° ’ W Lon 09° 28’.885 W Estimated depth: m Depth: m Date: 25/08/2007 Time: 21:14 GMT Gulf of Cadiz Mission

The trigger algorithm used for the seismometer is run by the GURALP digitizer DM24. In this standard algorithm two data windows of different length are used to calculate a STA/LTA (Short Time Average over Long Term Average), where the signal amplitude averages are taken over two running windows: The length in seconds of STW and LTW can be set by the operator. An event is detected when STA/LTA > RATIO where RATIO is a number indicating a threshold value set by the operator. The smaller RATIO is, the more sensitive is the algorithm, i.e. it will trigger for smaller magnitude events. STW- Short Term Window LTW- Long Time Window

Another important parameter the operator can set is the bandpass FILTER In our case we want the algorithm to trigger only for events that have M > Mx where Mx, the lower bound magnitude, is defined by the following constrains: It should be big enough so that the algorithm doesn’t trigger too often, using up the observatory’s batteries too quickly It should be small enough too detect a “sufficient” number of events during the experiment so the triggering system can be tested …….but this depends on the seismicity of the area….(and the background seismic noise level)…… So, to define the trigger parameters we consider……

NEAREST observatory Significant seismicity in the area of the Gulf of Cadiz (1960-present) Red circles are epicentres within 150 km of the ML5.9 From F. Carriho et al., Orfeus Newsletter, May 2007, vol. 7 No. 2

Distribution of recorded earthquakes over time Magenta line shows the chosen lower bound magnitude (Mx) for triggering From F. Carriho et al., Orfeus Newsletter, May 2007, vol. 7 No. 2

Then… We decided that Magnitude=3 is the lower bound magnitude We then decided to set the trigger parameters. To avoid triggering for small magnitude local earthquakes (i.e. Ml2.5) the FILTER parameters are set to perform a bandpass filter from 0.5 to 4.5 Hz The RATIO parameter is set to 11 (STW to 1s, LTW to 50 s) based on the following: Trigger algorithm was run on deep sea broadband (Guralp 360 s) recordings from the Ionian Sea (SN-1 site) from events of varying amplitude. This dataset was chosen given the similar recording instruments and conditions. Trigger algorithm was run on on-land recordings from the Portuguese seismic network (IMP). Recordings show efficient propagation of seismic waves- good S/N ratio. General considerations on earthquake energy scaling with magnitude.

Following the observatory’s deposition unexpected triggering of the seismometer took place  RATIO increased to 20 to make the algorithm less sensitive (and STW to 5 s). Furthermore an OBS (obs07) was deployed close to the observatory’s site, for almost 2 days (from about 10:30 of 29/08 to about 9:30 of 31/08), to have a quick look at the seismic signal and infer something about signal recorded by the observatory’s sensor. After the deposition we found out that at the same time there was an active seismic experiment (shot energy is recorded above 5 Hz- shot frequency about every 20 s) and initially the frequent seismometer triggering was thought to be caused by the shots. time (s) velocity (m/s)

Mission– experiment running but…..deviations from planning Mission– experiment running but…..deviations from planning Periodical checks – extraordinary check on the buoy sitePeriodical checks – extraordinary check on the buoy site Status of the activities (m 12) (task 4.3)

Time scheduling General WP4 Task 4.1 Provisional Actual xxxxxxx Task 4.2 Provisional Actual xxxxxxx Task 4.3 Provisional Actual xx Task 4.4 Provisional Actual xxx Task 4.5 Provisional Actual Present status of the activities (m 12)

Evidence that the buoy answered interrogation from VEGA – 17 October :58

Call to underwater modem attempted from VEGA

….connection with underwater modem from VEGA failed

Direct buoy link- Call on the buoy from Lisbon, positive response- 16 October 2007

Acoustic surface communication on-ship by the buoy site- configuration file correctly received by GEOSTAR-17 October 2007

Acoustic surface communication: Response to dacs status request command- -17 October 2007

Acoustic communication with the observatory is attempted……. 17 October 2007 ATS-V-USS (underwater) modem. Sending request (upload) of all values in particular: request of modem emission time parameter Management of

……failure in the acoustic communication with the underwater modem- Time out signal received indicates no answer from GEOSTAR acoustic modem

An analysis with the trigger algorithm on obs07 signal, deployed during the active experiment: there is no triggering with RATIO set to 20 (not even with RATIO set to 3). So it seems unlikely (also given the filtering in the algorithm Hz) that the shots started the initial triggering of the observatory sensor. This was confirmed by a recent visit to the buoy where the operator did not find any trigger messages from the seismometer during the active experiment: The only trigger found was of ‘pressure-type’, during an hour when a M=3.6 event at epicentral distance about 180 km fropm the observatory was recorded on land. The absence of seismometer triggers prompted us to revert to the original RATIO=12 value. The cause of the initial triggering is still unknown.

Deviations Anticipation of the cruise. Remedial action anticipation of Tasks (4.2, 4.3) Interference with the R/V Atalante seismic reflection experiment in the area: Remedial action: observatory software was properly reconfigured.

Atalante shot oceanographic cruise (info received from CNR-ISMAR) StartEndShot occurrence (s) Signal Freq. (Hz) Annotation DateTime (GMT) DateTime (GMT) 25 Aug. ‘07 01:4528 Aug. ‘07 9: s (50 m) Aug. ‘07 03:0009/Sept. ‘07 06: s (75 m) LON=6º ' W LAT=36º ' N (shot 1686-líne MF22)

Deviations Acoustic communications malfunctioning: Immediately after the GEOSTAR deployment, a final check on the communication systems (acoustics and satellite) was performed both from the ship board and from the land station in Italy. A malfunctioning in the communication system, namely the acoustic modem, was discovered Remedial action: the acoustic modem and the electronics of the buoy was removed and shipped to laboratory in order to set up again the communication chain. The system was restored and re-configured. On 17 October a new cruise has been planned in order to rebuild the communication on the buoy.

Deviations Inefficiency of the Globalstar satellite system coverage: by the early October, the Globalstar service provider (Elsacom) communicated that 4 satellites of the constellation failed. Remedail Actions: the service provider was contacted in order to solicit the restoration of the constellation. The provider has then communicated that 2 satellites will be again operating from late October while other 2 satellites will be restored by the second half of November.

Last week…. Buoy drift and ARGOS alarms emission to INGV (18 October) Extraordinary cruise for the buoy recovery (18-22 October) Buoy mooring cut and mooring cable at sea

Recovery of the buoy mooringRecovery of the buoy mooring Restoration of the buoy and deploymentRestoration of the buoy and deployment Integration of seismic data in the marine data-base of the OBS data (WP3 – seismological monitoring) (task 4.5)Integration of seismic data in the marine data-base of the OBS data (WP3 – seismological monitoring) (task 4.5) Work for the next period