Multidisciplinary Observatory Development in Monterey Bay
Debra Stakes, Paul McGill, Kenneth Johnson, Hans Jannasch
debra@mbari.org, mcgill@mbari.org, johnson@mbari.org, jaha@mbari.org
Monterey Bay Aquarium Research Institute, Moss Landing, CA

B. Romanowicz, D. Neuhauser
barbara@seismo.berkeley.edu; doug@seismo.berkeley.edu
Seismology Laboratory, University of California, Berkeley, CA

C. Geoff Wheat
wheat@mbari.org
University of Alaska, Fairbanks, AK and Monterey Bay Aquarium Research Institute, Moss Landing, CA

Abstract. The Monterey Bay Aquarium ResearchInstitute has several ongoing, parallel development
efforts that have a common goal of providing longterm multi-sensor measurements of ground motion
and fluid flow on the seafloor. Instrument packages
are being designed to operate in a low-power,
autonomous mode, but a planned logger/controller
will provide Ethernet connection to available cables
to either a shore-based laboratory or a telemeteredmooring. We describe here instrument deploymentsthat have taken place in the last four years (corehole
and broadband seismometers and chemical sensors)
as well as plans for the immediate future.
Corehole seismometers
Seismometer development was initiated at MBARI in
1996 with the development of a short-period corehole
seismometer, designed and fabricated by the JPL
Microdevice laboratory (Stakes et al., 1998). Thissensor package uses three standard 4.5-Hz geophones
with an extended flat response to about 0.8 Hz. The
sensor package is placed into 2.5 inch diameter
boreholes drilled into basement outcrops to provide
superior coupling and greatly reduced noise. A new
low-power datalogger, the GeoSense LP1, developedin 1997, can provide more than 24 GB of storage
using less than 0.3 watt of power, easily supporting a
12-month deployment.
During 1998, as part of the MBARI Margin
Seismology Project, an offshore network of fiveROV-installed instruments was continuously
deployed for 8 months. The corehole sensors wereplaced into holes in granite outcrops drilled by the
ROV diamond coring system. On sediment-coveredseafloor, the instruments were deployed within lowprofile cement "portable" boreholes. The data fromthese extended deployments have constrained the

distribution of seismicity on the off-shore segmentsof the San Gregorio fault (Fig. 1), identifying thenorthern San Gregorio as a zone of anomalous highseismicity(Begnaud and Stakes, 2000) withdominantly thrust focal mechanisms. An improved
local crustal velocity model permitted the relocationof all moderate events dating back to 1926 (Begnaud
et al., 2000). Based on these results, the southern San
Gregorio is apparently aseismic.
Because of their improved mechanical coupling, the
MBARI/JPL seismometers collect data in which theS-wave arrivals are resolvable for both large andsmall events. The capability to resolve the horizontal
shear waves as well as the vertical compressional
waves is critical to constraining the depth of theevents, especially for offshore events that typicallyhave large azimuthal gaps in coverage. Accurate
direct measurement of the sensor orientation by the
ROV combined with the well-displayed shear wave
data permitted consistent rotation of the horizontal
channels into radial and transverse components. This
allowed for more accurate shear wave arrival picks,
added phases for event relocations, and leads to moredetailed waveform analyses (Stakes et al, 2001)(Fig. 2).
During 2001-2, three of these corehole instruments
will be deployed to both supplement data from theland-based array and to provide developmental sites
for a planned logger development (the LP2). The
deployment sites include 1) the original MOISE siteon the center of the sediment-covered Smooth Ridge;2) the site MDUO where two boreholes are available
in extensive outcrop of Salinian granitic basement;
and 3) a new site southwest of Point Lobos andCarmel Bay (Fig. 1). The additional data from these
instruments will be useful to characterize any
microseismic activity from the southern segment of
the San Gregorio Fault Zone just offshore of the Big

Sur coast. We also hope to be able to refine thelocations and seismic activity of poorly constrained

segments of the Monterey Bay Fault zone justoffshore of MBARI.

Figure 1. Monterey Bay offshore of central California provides a unique site for testing long-term instrumentation. Short-period corehole
seismometers will be deployed during 2001 at three permanent sites. A new broadband observatory will be established on Smooth Ridge,
designated as the MOBB site. Chemical sensors and samplers have been deployed in the upper water column of Monterey Bay to characterizeseasonal upwelling events.

The corehole instruments will continue to be
deployed as autonomous packages until a) the LP1 isupgraded and b) a permanent cable or mooring isplaced into Monterey Bay.
Until a real-timeconnection is realized, the data from the instruments
will be recovered via ROV on a regular basis,
downloaded by MBARI and added to the publicdomain database. The data from multiple shortperiod instruments is useful for regional and local
tectonic studies such as these. The data become more
useful when used in conjunction with data from truly
broadband sensors.
Seismic Broadband sensors on the ocean floor
Figure 2. Example rotated waveforms for a regional teleseismic
event from the short-period sensor (MDUO) and the broadband
seismometer in Monterey Bay. The MDUO corehole instrument isdeployed in granitic basement rocks within the walls of Monterey
Canyon. The MOISE broadband sensor was partially buried in thesediment of Smooth Ridge west of the San Gregorio fault.

Methodology to deploy broadband seismic sensor
packages has been developed in collaboration withUC Berkeley. In the summer of 1997, a suite ofgeophysical instrument packages was deployed on
the ocean floor for 3 months using MBARI's ROV

Ventana, under the aegis of MOISE (Monterey Bay
Ocean Bottom International Seismic Experiment), aninternational cooperative pilot experiment between
MBARI, DT/INSU,IPGP and UBO (France) and UC
Berkeley.

contemporaneous logging of pressure and current
velocity documents that, during periods of low
bottom currents, the instrument noise is comparable
to land-based stations.
Chemical Sensors

The deployment site was in Monterey Bay, 40km
offshore and 10km west of the San Gregorio fault at awater depth of 1015m (Fig. 1). The instruments
deployed included: a three-component Guralp CMG3T broadband seismometer system, mounted onleveling gymbals, with a self-recentering program
designed by DT/INSU. The sensor package was halfburied in the sediments. The broadband wasconnected on the seafloor by the ROV to an LCHEAPO
recordingsystem(designedbyScripps/IGPP and modified by MBARI) and to an
external battery pack. A CTD/Paroscientific pressuregauge package and an S4 current meter were placed
nearby to measure local bottom currents. A standalone electromagnetic sensor package, contributed by
UBO was also deployed by the ROV and recovered
via elevator. In addition, two MBARI well-coupledcorehole seismometers were deployed at adjacentsites along with a variety of conventional shortperiod seismometers and hydrophones deployed as
stand-alone, contemporaneous measurements. On
three separate dives a connection was made from theship to the L-CHEAPO via the ROV RS232 withcommand and data links through the datalogger to theseismometer package. Through this link we were able
to a) successfully level and initiate the data collection
and recentering routines, b) extract samples of both
historical and real-time data to the state-of-health of
the system and c) re-level the seismometer sensors.
This experiment was, in particular, a successful
feasibility test for ocean floor deployment ofbroadband sensors using an ROV.
The seismic data from MOISE suggests that burial of
the broadband sensor package in the continental
margin sediments adequately reduces the noise frombottom currents. Both regional and teleseismic
events were usefully recorded (Romanowicz et al.,1998) at least in the "low-noise notch" (a frequency
band between 5-50 seconds) (Fig. 2)
The

Chemical sensor systems with long-term (order 1year) endurance and stability now exist for several
chemicals of relevance to hydrothermal systems
including sulfide, bromide and iron. These systems
can be deployed in an observatory network to couple
seismic, heat flow and chemical observations in an
integrated study of the processes that transport andtransform mantle energy into hydrothermal
ecosystems. For example, osmoanalyzers (Jannasch
et al., 1994) configured to determine dissolved ironhave been successfully deployed on Axial Seamount,monitoring Fe-variations in vent fluids (Fig. 3).
These systems have been deployed for time periods
in excess of one year.
New generations of
instruments, such as the In Situ Ultraviolet
Spectrophotometer (ISUS) are in development andwill greatly extend the range of chemicals that can bedetected in hydrothermal systems.
Chemical sensors will be supplemented byconventional physical sensors to measure temperatureand particulates adapted to the extended periods ofobservation. In addition, sampling devices will be
used to collect material for analyses that cannot yet
be performed in situ. These instruments include theOsmosampler (Wheat et al., 2000), which collects
small volumes of fluid into capillary tubes andprovides near daily resolution for time periods up to
14
12

Marker 33

10
Fe (µM)

The goal of MOISE was to advance the global
Seafloor Observatory effort through the development
and installation of a prototype suite of instruments
placed on the western side of the San Andreas fault
system offshore of Central California (Stakes et al.,
1998; Romanowicz et al., 1998). The centerpiece ofthe MOISE instrument suite was a digital broadband
seismometer package partially buried within thesediment-covered floor of Monterey Bay.

8
6
4
2
0
25-Aug-99

27-Aug-99

29-Aug-99

31-Aug-99

02-Sep-99

Figure 3. An Fe-Osmoanalyzer was deployed at ambient
temperatures on Axial Seamount on the Juan de Fuca Ridge with
its intake (~2m long) positioned about 40 cm below the surface
inside the hydrothermal vent near “Marker 33” (~1500m). The FeOsmoAnyalzer provided continuous analysis of Fe concentrations
with readings recorded every 15 minutes. The analyzer selfcalibrated itself by analyzing known standards every 10 days, andoperated continuously from June 1999 until June 2000. The main
variability correlates with tides (Jannasch et al., 2000).

five years. Other, more complex, fluid and microbial
samplers have yet to be adapted to seafloor
deployments.

data logger, CTD, current meter and pressure gauges(Fig. 4). The sampling rates for the instruments will
be better matched to permit some removal of thebottom current noise (e.g. Stutzman et al, 2001).

The Future
MOBB, MOOS and Neptune
As a follow-up to the MOISE experiment, in acooperative project between MBARI and UC
Berkeley, with complementary support from NSF, weare currently planning the permanent deployment of abroadband, three-component seismometer package inMonterey Bay. The deployment will comprise a
Guralp CMG-1T sensor package, a modified LP1
brought as close to zero as possible.

The CMG-1T broadband seismometer has a flat
velocity response from 360 sec to 50 Hz and lower
instrumental noise than the CMG-3T, the sensor usedin the 1997 MOISE experiment. It is equipped with aremote automatic mass locking, mass unlocking andcentering capability. The Guralp +/-30 degreeleveling system is especially designed for use withlong-period broadband sensors. The radial andazimuthal adjustments are done until the two-axes
inclinometer
outputsareFigure 4. Schematic of the plans for the MOBB deployment site. The Guralp sensor will be fully buried in sediment. Ancillary sensors will
include an absolute and a differential pressure gauge.

The position detectors are absolute and position
information is retained even when the system isswitched off. It operates without leveling up to +/2.5 degrees of tilt. The CMG-1T sensor mass has
been increased (compared to the CMG-3T) to 250gm
to reduce the Brownian noise of the system. The
vertical sensor inertial mass and the inverted
horizontal pendulum are both supported with leaf
springs with a natural period of about 0.9s. The 24bit A/D converter module DM24 is mounted on topof the sensor housing and provides standard RS232
output. The internal clock will utilize an external 1

pulse per second signal from the LP1/2 to control thedigitizing rate and provide reference for the timestamps.
Although the MOISE instruments were deployed only
for a few months, the strategies invoked for theirinstallation emulated those adopted for permanent
deployment of the MOBB instrument. Thesemethodologies include: in situ assembly of instruments
using
underwater
connectors
manipulatedbysubmersibles, improved coupling of sensors by burial or
borehole installation, repeated access to sensor data
during the experiment, and the addition of externalbattery packs to extend the instrument deployment
period. The sensor package for MOBB will becompletely buried to minimize the impact of thebottom currents. The weighted cable from the sensor
will be connected to an LP1 data logger and an
external battery pack, both of which will be in trawlresistant structures (Fig. 4).
The deployment is planned for September 2001. The
MOBB site will be prepared by the ROV using awater jet to dig a hole and sink a caisson large
enough for the sensor. The instrument will be carried
to the seafloor by the ROV with the sensors in thelocked position and then placed within the caisson.
The data logger and external battery pack will be sent
to the seafloor via elevator and connected by the
ROV. The sensors will be unlocked and initiallyleveled manually via the RS232 connection with the
ROV. The ROV will confirm proper operation of thesystem and then the automatic leveling and centering
programs will be initiated. During the regular visits,
the sensor package will not be disturbed. The datalogger and external battery packages will be replaced
by ROV. The permanent broadband station will be
the first seafloor node for the Berkeley Digital
Seismic Network (Romanowicz et al., 1993).
Initially, this instrument will operate autonomouslywith batteries and data transfer conducted during
ROV dives, configured to operate stand-alone for atleast 1 year.
It is anticipated that the MOBB will ultimately
benefit from other, ongoing MBARI efforts toprovide continuous real-time telemetry back to theshore-based laboratory. The connection to a MOOS
(MBARI Ocean Observing System) mooring will
provide the data link for the offshore site to provide
continuous data on regional and teleseismic events.
The data will be available through the NCEDC(Northern California Earthquake Data Center) at UC
Berkeley. Monterey Bay will also be the site of a
NEPTUNE test-bed that will provide a cabledconnection to the seafloor instruments networked by
ROV-laid fiber. The test-bed will exploit the samemechanical interfaces and data protocols as the
proposed cable encircling the Juan de Fuca Plate(Delaney, J.R., et al., 2000).
The LP2 Logger/Controller and Networked“Smart” Experiments.
In 2001, the LP1 will be upgraded by replacing theMotorola 68332 microprocessor with an Intel
StrongARM microprocessor. The new logger, called
the LP2, will have significantly enhanced processing
capability with only a slight increase in power

consumption. The LP2 will be able to run complex
processing algorithms in situ, such as seismic event
detection and location. The LP2 will also have an
Ethernet port, which will enable connections to undersea
networks and allow rapid downloading of recorded data.
During the next two years our goal will be to interface
multiple sensors to the LP2 logger/controller for studiesof fluid flow in volcanically and tectonically active
sections of the mid-ocean ridge. For our studies ofdeformation and fluid flow, the contemporaneous
measurement of both chemical and seismic activity isessential. We envision the LP2 as the core of a miniobservatory to operate in an autonomous mode or as amultiple-sensor node on a larger, cabled experiment.
Advanced software protocols will eventually operate
either within the LP2 controller, within the MOOS
central hub, or at the NEPTUNE test-bed to allow in situ
data processing for event recognition and response. Thiseffort will combine the achievements of the seismology
efforts with new chemical sensors developed at MBARI
and MOOS. This successful completion of this effort will
be a milestone in the establishment of long-term seafloor
experiments with real-time connections to land.
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