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Applications of Ocean Acoustic Monitoring to Understanding our Planet

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Title: Applications of Ocean Acoustic Monitoring to Understanding our Planet


1
Title
Applications of Ocean Acoustic Monitoring to
Understanding our Planet
2
Outline
Applications of Ocean Acoustic Monitoring to
Understanding our Planet
  • How we listen
  • What we hear
  • Great Sumatra-Andaman Earthquake
  • Mid Ocean Ridge Earthquakes

3
Physics of sound travel
PHYSICS OF SOUND TRAVEL IN THE OCEAN
The physical properties of seawater affect the
transmission of sound. The speed of sound
decreases with decreasing temperature and
increases with increasing pressure. The
relationship of these two properties results in a
zone of minimum sound velocity in the ocean
referred to as the SOFAR (SOund Fixing And
Ranging) channel. The SOFAR channel acts as a
waveguide, trapping energy within it, and
allowing efficient propagation of sound, with
relatively little energy loss compared to the
solid earth.
4
RECORDING OCEAN EARTHQUAKES
RECORDING OCEAN EARTHQUAKES OTHER SOUNDS
Primary advantages of hydroacoustics - Low cost
coverage on ocean scale - Lowers magnitude of
completeness to 3.0 mb -Travel path extremely
well known (1.485 km/sec) -For very large events,
t-wave isnt buried in secondary arrivals
3 complementary scales of observation
5
HYDROPHONES
LISTENING WITH HYDROPHONES
6
SOFAR USE
SOFAR USE
The SOFAR channel is believed to be used by some
marine mammals to communicate. It has also been
used by the Navy for decades for a variety of
purposes involving submarines. Some say it won
the cold war
Scientists are now using it to monitor seafloor
earthquakes, marine mammal calls and other noises.
7
Science Goals
SCIENCE GOALS FOR HYDROACOUSTIC MONITORING
  • SEISMOLOGY Local, Regional and Teleseismic
    earthquakes can be used for solid earth research.
    This includes mapping the internal structure of
    the planet, monitoring large earthquakes for
    local or distance impacts, understanding the
    structure of plates and studying mid-ocean ridge
    processes.
  • BIOLOGY Identify marine mammal populations in
    the area, allowing for stock assessment, and
    migration studies. Also provides potential
    examples of regional differences in call for
    globally distributed species.
  • OCEAN NOISE Address call from recent National
    Academy of Sciences report for assessment of
    Global Ocean Noise budget at broad range of
    frequencies. These arrays can provide
    quantitative assessments of different sources
    such as ice movement, shipping, geophysical
    (anthropogenic natural), weather related, and
    marine mammal at low frequencies.
  • EXPLOSION MONITORING Assist in monitoring the
    Comprehensive Test Ban Treaty Characterize
    sound sources, understand blockage phenomenon.

8
GLOBAL HYDROPHONE ARRAYS
GLOBAL HYDROPHONE ARRAYS
9
Earthquakes
EARTHQUAKES
T-wave water-borne phase characterized by
emergent arrivals coda
x 20
10
Iceberg drift
ICEBERG DRIFT
Chapp et al. 2005
11
CPTS
ICE STREAMS
x 20
12
Migration of Antarctic Blue Whales
Migration of Antarctic Blue Whales in the Indian
Ocean Basin
From Stafford et al. 2004
x 20
  • Major Observations
  • Antarctic Blues migrate as far north as DG
  • Limited to Austral Winter

13
Anthropogenic noise sources
ANTHROPOGENIC NOISE SOURCES
14
Anthropogenic noise and marine mammals
ANTHROPOGENIC NOISE AND MARINE MAMMALS
NEED MORE DATA..
15
2002 INDIAN OCEAN SIGNALS
2002 INDIAN OCEAN SIGNALS
16
INDIAN OCEAN IMS HYROPHONE STATIONS
INDIAN OCEAN IMS HYDROPHONE STATIONS
17
THE GREAT SUMATRA ANDAMAN EARTHQUAKE
THE GREAT SUMATRA ANDAMAN EARTHQUAKE
26 December 2004 0058 GMT - Magnitude 9.3
18
Tsunami title
Constraining the rupture length, duration and
speed of the Great Sumatra-Andaman Earthquake
Apparent duration 800 seconds Corrected for
path differences 480 seconds
19
Azimuth Calculations
AZIMUTH CALCULATIONS
To identify T-wave radiator locations, azimuthal
estimates are derived by inverting the
differential travel times between sensors within
the DGS hydrophone triad. Travel time
differences between each pair of hydrophones
within the stations triad were derived from the
cross-correlation of the 4-6 Hz bandpassed signal
arrivals, within 10 second windows having 50
overlap.
Yields azimuthal accuracy on the order of 1
degree or less.
20
Final azimuth
AZIMUTHS
21
Locating t-wave radiator
LOCATING T-WAVE RADIATOR
Projecting the azimuths onto the 2000 m contour
provides an estimate for the t-wave radiator
position. This position was corrected back onto
a theoretical fault line using the track of the
trench fault and a 6 km/s crustal velocity
correction. This was in an effort to account
for the topographic meandering at 2000 m that
likely was not related to fault plane. (For
shallow source at e.g. Mid-Ocean Ridge, location
based on multiple stations can be good estimate
for epicenter - for deeper or shelf events,
radiator location may be different at different
azimuths).
22
Where did it stop
WHERE DID IT STOP?
Pole of rotation
23
RUPTURE AREA
RUPTURE AREA
Earthquakes rupture a patch along fault's
surface. Generally speaking, the larger the
rupture patch, the larger the earthquake
magnitude. Initially believed that just the
southern portion of the fault slipped, but more
recent data suggests entire aftershock area
slipped. Area the size of California. For
comparison, a magnitude 5 earthquake would
rupture a patch roughly the size of New York
City's Central Park.
24
Speed of rupture
SPEED OF RUPTURE
Two-phase process?
25
Amp vs. Lat
AMPLITUDE VERSUS LATITUDE
26
Conclusions
SUMMARY - GREAT SUMATRA-ANDAMAN EARTHQUAKE
  • - Rupture length 1200 km
  • - Duration 8 minutes
  • - Velocity 2.7 km/s to 2.2 km/s ( 0.2)
  • - Two-phase process
  • - Rupture ends at plate boundary change.
  • T-waves useful for rapid determination of size
    and scope of very large submarine earthquakes.
  • (Tolstoy et al., 2005)

27
MID-OCEAN RIDGES
MID-OCEAN RIDGES
- 2/3rds of the surface of our planet formed at
Mid-Ocean Ridges. - Different spreading rates
yield different MOR features. - Prior to 1993,
we had very little information on what a
(seafloor) MOR eruption looked liked.
28
HYDROTHERMAL VENTS
HYDROTHERMAL VENTS
Planetary Renewal and Life in the deep ocean
From Mantle to Microbe
http//www.Ridge2000.org
29
IMPORTANCE OF EARTHQUAKES AT MID-OCEAN RIDGES
IMPORTANCE OF EARTHQUAKES AT MID-OCEAN RIDGES
Mid-ocean ridges are where 2/3rds of the
surface of our planet is formed. Earthquakes
represent fundamental perturbations to the MOR
systems. They can provide an influx of
nutrients. The eruptions (associated with
earthquakes) are building blocks of the planet
and a time zero for the biological communities.
Earthquakes are a basic driving force of life,
providing a route for nutrients and heat.
30
ERUPTION SPECTRA
ERUPTION SPECTRA
No large mainshock swarm doesnt obey Omoris
Law often migration.
31
ERUPTION CONSEQUENCES
ERUPTION CONSEQUENCES
Fresh Lava
Bacterial Floc
32
Known eruption sites
1 Gakkel - Arctic 1999
4 eruptions Juan de Fuca Ridge since 1993
1 MAR since 1999
4 eruptions equatorial EPR/Galapagos Rise since
1996
1 SEIR 2003
A trend appears?
33
320 EPR location
320N EPR
34
320N EAST PACIFIC RISE
320N EAST PACIFIC RISE
latest
Two events recorded globally (magnitudes 3.7
4.1). Most events seen only on hydrophones.
later
earlier
Activity lasted 1 week, peak activity 24
hours.
35
97.5 location
97.5 W Galapagos Rise
36
97.5 W GALAPAGOS RISE
97.5W GALAPAGOS RISE
Lasted 13 days, peak activity 3 days 9
teleseismic events
37
Gakkel Ridge
38
GAKKEL ERUPTION
GAKKEL RIDGE
Remote and isolated, we still dont know what
lives there..
39
Event Characteristics
EVENT CHARACTERISTICS
  • - 1999 a MEGA Event
  • - All earthquakes recorded globally.
  • Activity lasted 7 months. Peak activity lasted
    3 months.
  • (Tolstoy et al. 2001)

40
ERUPTIONS SCALE WITH SPREADING RATE
ERUPTIONS SCALE WITH SPREADING RATE
Perfit Chadwick 1998, Sinton et al. 2002 -
Eruption volume scales with spreading rate.
Chemical heterogeneity increases with decreasing
spreading rate (Rubin et al. 2001, Sinton et al.
2002). (rel. to thermal stability)
41
PDE Epicenters
LOOKING FOR LIFE IN THE DEEP OCEAN
Earthquakes are a good indicator of where to look
for life in a relatively barren environment.
42
ELSEWHERE IN THE SOLAR SYSTEM
ELSEWHERE IN THE SOLAR SYSTEM
  • Where there are earthquakes there is more
    likely to be life. So to find life elsewhere in
    the solar system we should look for the
    earthquakes. (Tolstoy et al. 2004, NASA White
    paper)

43
SUMMARY
CONCLUSIONS
There is a lot we can learn from listening to the
ocean We are still in our infancy of
understanding seafloor processes and acoustic
signals in the ocean.
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