Paroscientiﬁc 社が開発したナノ分解能（1/1,000,000,000FS）を有した水晶振動式圧力センサーに関する実海域（MARS サイト）における評価レポート

Paroscientiﬁc 社が開発したナノ分解能（1/1,000,000,000FS）を有した水晶振動式圧力センサーに関する実海域（MARS サイト）における評価レポートです。従来の水晶振動式圧力センサーとナノ分解能の圧力センサーを比較し、ナノ分解能の圧力センサーが検知した近地震、遠地地震、微小津波などの事例を紹介します。

ナノ分解能の圧力センサーが開発され、広い周波数範囲にわたって、これまでにない精度で圧力変化を測定することができるようになりました。日本では主に火山活動を監視する微気圧計（インフラサウンドセンサー）として多く用いられています。

一方このレポートの様に海底観測において、ケーブル観測装置 MARS では、微小津波、地震、微小地震、重力波の高分解能圧力測定が可能であることが実証されています。これらの成果は、近地津波の予測精度の向上につながることが期待されています。

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Nano-resolution technology demonstrates promise for
improved local tsunami warnings on the MARS
project
J. Paros, P. Migliacio, and T. Schaad

C. Meinig, M. Spillane, L. Tang, and S. Stalin

Paroscientific, Inc.
Redmond, Washington U.S.A.

NOAA/Pacific Marine Environmental Laboratory
Seattle, Washington U.S.A.

W. Chadwick
Oregon State University
Newport, Oregon U.S.A.
Abstract— Recent advances in deep-ocean tsunami measurement
technology coupled with tsunami forecast models have reliably
demonstrated that tsunami impact can be predicted before thetsunami reaches the affected coastlines. These forecast models arebased on observations that are typically 1000 km or more fromthe earthquake epicenter. The major challenge today is toforecast tsunamis in the near field where the tsunami wave isoften overwhelmed by the seismic event. Nano-resolutionpressure sensors have the necessary resolution to distinguishbetween tsunami and seismic signals and ocean noise in the nearfield. This study describes the results of a 17 month experimentthat was initiated on June 30, 2010, at the Monterey Accelerated
Research System (MARS) cabled observatory in Monterey Bay,
California. The experiment compared a conventional pressuresensor and a nano-resolution pressure sensor at a depth ofapproximately 900 m. The results presented include examples ofnear- and far-field earthquakes and micro-tsunamis that weredetected by the nano-resolution pressure sensor. Throughwavelet analysis several micro-tsunamis were identified. The
paper also describes additional testing planned by NOAA on thenano-resolution pressure sensors for potential application to theNOAA DART System.
Keywords-Tsunami, warnings, DART, BPR, pressure,measurement, nano-resolution, cable, observatory, MARSI.

INTRODUCTION

This paper updates and expands upon an experiment
performed at the Monterey Accelerated Research System(MARS) cabled observatory in Monterey, California [1].
Deep water (up to 6000 m) distant tsunami detection
capability has been demonstrated by the NOAA (NationalOceanic and Atmospheric Administration)-led U.S. NationalTsunami Hazard Mitigation Program [2]-[6]. One of theremaining challenges is to forecast tsunamis in the near field
where the tsunami signal may be obscured by earthquake
vibrations and other ocean “noise” not commonly found atdeep water installations.
New high-resolution pressure sensors have been developedthat can distinguish between earthquake, ocean “noise” and978-1-4577-2091-8/12/$26.00 ©2011 IEEEtsunami frequencies without losing precision. Improved counting
techniques can measure the frequency outputs of quartz
resonator sensors to parts-per-billion precision (nano-resolution).
See: http://paroscientific.com/Nano-Resolution.pdf. All nanoresolution measurements taken in this paper use nano-resolution
counting with multi-stage digital IIR low pass filters [7].
A nano-resolution pressure sensor was incorporated into ageophysical instrument package that was already funded by
the National Science Foundation (NSF) and underdevelopment by Oregon State University (OSU) andNOAA/Pacific Marine Environmental Laboratory (PMEL).
The original OSU/PMEL instrument was designed forsubmarine volcano monitoring and included high- and lowresolution tilt sensors and a standard bottom pressure recorder(BPR) for detecting vertical displacements of the seafloor due
to volcanic inflation/deflation [8]. Part of this project was totest the instrument for one year on the MARS cabled
observatory, located in Monterey Bay, California, andoperated by the Monterey Bay Aquarium Research Institute(MBARI). MARS is a test bed for instrumentation that could
be used by NSF’s Ocean Observatories Initiative (OOI)(http://www.mbari.org/mars/general/about_mars.html). Fig. 1
illustrates the location of the MARS test bed. The OSU/PMELinstrument was designed to be eventually deployed at Axial
Seamount, an active submarine volcano that will be a node on
the cabled observatory component of the OOI in the NE Pacific(http://www.interactiveoceans.washington.edu/).
During the development of the OSU/PMEL instrument, anano-resolution pressure sensor was added, through acollaboration of NOAA-PMEL, University of Washington, andParoscientific, Inc., in a joint effort to demonstrate the capability offorecasting tsunamis in the near field using this new technology.
The OSU/PMEL instrument package was deployed on the MARS
cable on June 30, 2010, at a depth of approximately 900 m. The
experiment and analysis compared a standard NOAA BPR(http://nctr.pmel.noaa.gov/Dart/Pdf/DART_II_Description_6_4_05.pdf) to the nano-resolution pressure sensor. Both sensors
are installed on the same tripod platform as shown in Fig. 2.

Figure 1. The Monterey Accelerated Research System (MARS) cabled observatory is located in Monterey Bay, California. Please see
http://www.youtube.com/noaapmel#p/u/0/iq9IxQPBQcc for a short video on the experiment.

II.

DATA FROM THE MONTEREY ACCELERATED RESEARCHSYSTEM (MARS) EXPERIMENTThe new nano-resolution pressure sensor, manufactured by
Paroscientific, Inc., has several orders of magnitude higher
resolution than a traditional sensor installed in a NOAA BPR.
While power requirements of the nano-resolution sensor are
higher, it is also capable of recording data at much higher
sampling rates. This unprecedented resolution allows scientists
to better distinguish between oceanographic signals/noise andseismic events for improved tsunami detection and modeling.
The Nano-resolution pressure sensors are able to measureocean signals with fine scale clarity, including the detection ofmicroseisms, infra-gravity waves and earthquakes. The plot inFig. 3 compares the standard NOAA BPR to a nano-resolutionpressure sensor. The nano-resolution pressure sensor is able todistinguish pressure changes equivalent to a fraction of amillimeter that are the result of microseisms and longer-period
infra-gravity waves.

The nano-resolution pressure sensor can be configured
through software commands to change the measurement
parameters, and it was co-located with a standard resolution
NOAA BPR to enable comparative measurements between thetwo. This experiment has shown that seafloor measurements ofabsolute water levels, tides, infra-gravity waves, microseisms,
and signals from distant and nearby earthquakes can be madewith greater accuracy than with previous instrumentation.
Earthquakes can produce dynamic pressure variations,which are infrasonic acoustic waves. These waves, produced
by local earthquakes with magnitudes as low as 3.0, have been
detected by the nano-resolution pressure sensor at MARS. At
longer periods, the entire water column above the sensor moves
up and down in response to the passing tsunami wave train
with an amplitude that can be computed from the seafloorpressure fluctuations with the scaling P = ρ g h (water density,gravity, and height). Accurate time series of a tsunami signal,
for comparison with pre-computed model scenarios, are thebasis of the forecast system [3]. The high-frequency earthquake
signal is noise for the tsunami detection process. With standard
sensors, this noise overwhelms the tsunami signal, making
tsunami detection difficult. The improved temporal sampling
and vertical accuracy provided by nano-resolution pressure
sensors shows promise for tracking the earthquake vibrations
while recording the tsunami signal, opening the possibility ofearlier near-field tsunami detection.
III.

EARTHQUAKE DETECTION

Data from the M5.4 earthquake near Palm Springs on July
7, 2010, at 23:53:33 was analyzed. The arrival of the p-waves
from this earthquake coincided with seismic data from thenearest land-based station at San Juan Grade (see Fig. 4). The
largest amplitudes were equivalent to +/- 8 mm water height(however, it would have been larger with a higher low-passfilter cutoff in the counting algorithm).
Figure 2.

OSU/PMEL BPR/Tilt instrument showing relative placementof nano-resolution and standard BPR sensors.

Figure 3. Nano-resolution pressure sensor data are shown (in blue on lower plot) hours after initial deployment. The overall pressure is rising from anincoming tide. Near 0.2 Hz, the data is dominated by microseismic acceleration of the seafloor (equivalent to 1 mm pressure variations). At longer periods,
near 1 minute, pressure variations of a few millimeters water heights are from surface waves that are detected at the deployed depth of 900 m. The red data
are from the co-located standard tsunami sensor at much lower sampling rate (15 seconds) and resolution (but still capable of resolving typical 1 mm waves
at long periods). Note: the plots are arbitrarily offset to allow the reader to see differences in plotted data.

Figure 4. The upper panel shows consecutive 15-minute segments of the nano data (detrended) that correspond to the similarly colored traces in theUSGS record from San Juan Grade in the lower panel. Inset is a locater map for the two locations which are separated by about 56 km. Vertical lines in
red show the earthquake time and the arrival at the seismometer. The nano-resolution pressure sensor begins to respond a couple of minutes later and its
earthquake signal has a similar duration to the land-based instrument.

IV.

DISTANT MICRO-TSUNAMI DETECTION

A micro-tsunami was recorded by the nano-resolutionpressure sensor on December 21, 2010 (M7.4 Bonin Island
earthquake). Using wavelet analysis, spectrograms werecomputed (see plot in Fig. 5 below). The cutoff period for tide
removal is 1 hour, using Butterworth filters. Note the color
scale in the plot was set to emphasize the tsunami, so the highfrequency components are muted. The red line is the modeled
tsunami amplitude time series. In Fig. 5, the tsunami appears
from 645 to 745 minutes (indicated by white dashed line) witha period of about 14 minutes and a maximum tsunami
amplitude of about 0.2 cm.

V.

MARCH 11, 2011 HONSHU EARTHQUAKE AND
SUBSEQUENT TSUNAMIOn March 11, 2011, a huge M9.0 earthquake occurred off ofthe northeast coast of Japan. The earthquake was centered off
the Pacific coast of Tōhoku and is known as the 2011 Tohoku
earthquake. The megathrust event occurred at 14:46 JST (05:46UTC). The epicenter was approximately 70 km (43 mi) east ofthe Oshika Peninsula of Tohoku. The earthquake triggered
powerful tsunami waves that reached heights of up to 40.5 m(133 ft) in Miyako, in Tōhoku's Iwate Prefecture, and which, inthe Sendai area, travelled up to 10 km (6 mi) inland. Theearthquake moved Honshu 2.4 m (8 ft) east and shifted theEarth on its axis by estimates of between 10 cm (4 in) and 25cm (10 in).

Figure 5. A micro tsunami generated by the M7.4 Bonin Island Earthquake on December 21, 2010 was recorded by the nano-resolution pressure sensor. (a) The
black line is the nano-resolution observations with tides removed by a Butterworth filter with a cutoff period of 1 hour. The red line is the modeled tsunami
amplitude time series. (b) Wavelet-derived amplitude spectrogram of the observations. The white dashed line indicates the existence of the tsunami signals.

At approximately 15:40 UTC, the wave arrived in Monterey
Bay, California, at the MARS cabled observatory. The nanoresolution pressure sensor recorded a wave height ofapproximately 25 cm as shown in Fig. 6. Prior to the arrival of thewave the pressure sensor was detecting small microseisms at thetypical background level.
VI.

LONG-TERM MEASUREMENTS

Both the standard bottom pressure transducer and the nanoresolution pressure sensor contain internal digital temperature
sensors for thermal compensation. The pressure sensors areFigure 6. Nano-resolution pressure sensor at 40 Hz measures a 25 cm
tsunami wave in Monterey Bay, California, which was a result of theHonshu, Japan earthquake on March 11, 2011.

calibrated over a broad range of temperatures, and the outputsof the quartz pressure-sensing crystal and quartz temperaturesensing crystal are measured. Coefficients are calculated for
insertion into an algorithm to generate fully temperaturecompensated and linear pressure outputs. Fig. 7 plots pressure
and temperature for about one month of data for both thestandard BPR and the nano-resolution pressure sensors. As
shown in Fig. 2, the nano-resolution pressure sensor is exposed
directly to the seawater, whereas the standard pressuretransducer is contained within the BPR housing with additional
electronic equipment. As a result, the temperature within theBPR housing is higher by about 3.5°C. The packaging also
affects dynamic temperature behavior whereby thermal
gradients can cause pressure errors. The transient “spikes”
shown in red in Fig. 8 for the standard BPR were caused byloss of power and subsequent warm-up effects. The nanoresolution pressure sensors showed little effect due to thereduced thermal effects from the power conditioning
electronics.
Fig. 8 shows the de-tided pressure records (converted todepth) for the nano-resolution pressure sensor and standard
BPR for the entire 17 month deployment. Not only was thenano-resolution pressure sensor insensitive to the dynamic
thermal effects of warm-up after power outages, but it showed
no discernable drift. The standard BPR had a drift rate of 21 cm
per year equivalent to 30 parts-per-million of full-scale range(7000 m). The nano-resolution pressure sensor in the MARS
tests has a full-scale range of 1400 m. The absolute drift rate
(cm per year) is a strong function of full-scale range. Therefore,
the highest resolution and best stability is achieved when thepressure transducer range matches the deployment depth.

Figure 7. Pressure and temperature measurements of nano-resolutionpressure sensor and standard BPR. The spike in the BPR de-tided depth timeseries (red) is due to transient temperature effects (orange) after a power
cycle. In contrast, the spike in the nano-BPR de-tided depth time series(dark blue) is due to a known timing error and mismatch with a tide
prediction model

Figure 8. Pressure data (converted to depth) from nano-resolution presure
sensor and standard BPR over the entire 17 month deployment at MARS.
The spikes in the BPR time series (red) are due to transient temperatureeffects after a power cycle. In contrast, the spikes in the nano-BPR timeseries are due to a known timing errors and mismatches with a tide
prediction modelVII. POTENTIAL APPLICATION TO NOAA DART SYSTEM
Research and development is continuing on special versionsof the nano-resolution technology [7] that are being consideredfor incorporation into future near-field NOAA DART systems,
The near-field system will build on proven DART performanceand will be enhanced to provide high-resolution, userconfigurable, multi-mode, low-power, and extended-lifetsunami warning systems.

[2]

[3]

[4]

VIII. CONCLUSIONS
Nano-resolution pressure sensors have been developed withthe capability to measure pressure changes with unprecedented
precision over an extended frequency spectrum. Tests at theMARS cabled observatory have demonstrated the ability tomake high-resolution pressure measurements of microtsunamis, earthquakes, microseisms, and infra-gravity waves.
These developments hold promise for improving forecasts fortsunamis in the near field.

[5]

[6]

[7]

ACKNOWLEDGMENT
This project was funded by a grant to Oregon State
University from the National Science Foundation (award OCE0826490). We thank MBARI for excellent logistical support
during deployment and recovery of the instrument and for
operating the MARS cabled observatory.
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