Evaluation of the ASHE Project, Ecuador

M. Garcés1, D. Fee1, and A. Steffke1 D. McCormack2 and R. Servranckx3

H. Bass4 and C. Hetzer4

M. Hedlin5 and R. Matoza5

H. Yepes6 and P. Ramon6

1Infrasound Laboratory, University of Hawaii at Manoa2Geological Survey of Canada, 1 Observatory Crescent, Ottawa K1A 0Y3 Ontario, Canada

3Montréal Volcanic Ash Advisory Centre, Canadian Meteorological Centre, Meteorological Service of Canada

4University of Mississippi5University of California, San Diego

6Instituto Geofísico, Escuela Politécnica Nacional,Quito, Ecuador ITW, Bermuda, 2008

Bolides – low mass, hypersonic (10’s of km/s) short duration, broad band, moving source(s) distributed in space (line)

Microbaroms - high mass (moving swaths of ocean), low velocity (m/s), nearly continuous, narrow band, multiple moving sources distributed in space (areas).

Surf – medium mass, low velocity (10’s m/s), sustained over periods of days, broadband, multiple moving sources distributed over coastal areas.

Volcanoes – high mass (erupted volumes of cubic km), medium to high speeds (up to ~Mach 1), impulsive to continuous durations, narrow and broadband signals, well localized surface source (point). Stationary in space, but very nonstationary in time.

Due to substantially different physics, energy estimates for ocean and volcanic processes do not lend themselves well to equivalent yield scaling. Propose use of Watts and Joules for continuous and impulsive events, respectively. Well suited energy units for comparison with satellite methodologies. Acoustic to electrical energy efficiency for speakers is typically ~1-10%.

Efficient Geophysical Infrasound Sources Routinely Detected by IMS

TRANSIENTS:

Explosions - impulsive, bipolar pulses with durations of seconds.

Long Period events - possibly emergent events sustained for seconds to minutes. Spectral peaks in 0.5-5 Hz band.

Very Long Period Events - pulses in the 0.5 – 0.001 Hz band

TREMOR/JETTING:

Near continuous oscillation sustained for minutes to years.

Volcanosonic signals

ASHE EcuadorInstrumentation

RIOE

LITE

MACE

Sangay

Tungurahua

Reventador

Galeras

Ecuador

RIOE Tungurahua: 37 km

LITE Tungurahua: 251 km

Automatic explosive event identification•Time period: 2/15/06- Fall 08

•Automatically calculate azimuth, amplitude, duration, and acoustic energy

•>20,000 explosions at RIOE (37 km)

•>3500 explosions at LITE (251 km)

• High-pass filter data >.5 Hz

•STA/LTA event onset and end time 2/5 secs, 3/40 secs Detection must be on all 4 channels

•

Run PMCC between 0.5-4 Hz

10 bands, 10 sec windowsFamilies with correct azimuth (±7°) Minimum family size and amplitude

Explosions

Range of 5 km, 40 km, and 250 km.

Near field data courtesy ofKumagai and Molina, 2008

Localization• No obvious cutoff amplitude

• Picked up everything over 0.7 Pa, but missed a few around 0.6 while picking up some as small as 0.2 Pa

• Detection may depend on local noise and high-altitude wind

Using thermospheric arrivals for LITE and direct path for RIOE

mean error (km) = 2.5518Mean delta lat = 0.0086Mean delta lon = -0.0051

Using stratospheric arrivals for LITE and direct path for RIOE

Mean error (km) = 6.7821Mean delta lat = 0.0534Mean delta lon = 0.0281

Diffraction zone!

Case Study: 8/16-17 2006

• Main Eruption: 1930-0620 UTC Total Duration ~10.8 hours

•VEI 4 eruption inferred from satellite estimate of ash height

•>20 pyroclastic flows and up to 6 km lava fountain!

•Intense jetting (±5 Pa at 37 km)

•Ejection of dark, ~24-km high, ash-laden plume.

System Training: Case Study of 8/16-17 2006

Growing list of case studies compare satellite-derived ash heights with acoustic signal intensity and character derived from arrays. Used fine-scale atmospheric

specifications typically used for sound propagation studies.

System Training: Case Study of 8/16-17 2006

Spectrogram for the Plinian phase of the 8/16 eruption. Note the increase in energy and decrease in frequency of the signal around 0530 UTC. The

frequency axis is plotted on a logarithmic scale.

Training Set: Tungurahua Eruption PSDs

Sustained Signal Identification and Monitoring• Automatically posted on web page

• Free Space Acoustic Energy:

EAcoustic=2πr2/ρc ∫ΔP(t)2dt r=source-receiver distance ρ=air density c=sound speed ΔP=change in pressure

• Acoustic power = Energy/time

• To minimize the effects of wind noise, the acoustic energy was calculated above 0.5 Hz (reprocessed above 0.1 Hz for some signals)

• Acoustic energy only calculated if PMCC results corresponded to significant acoustic signal arriving from ±7° of Tungurahua

Ops: Automatic Eruption Notification of 2/6/08

ASHE Activity Notification

ASHE Explosion Notification

Spectrogram, Acoustic Source Power, and Ash Cloud Height

Used coarse atmosphere

5-minute notification latency!

Okmok and Kasatochi Detections by IMS stations: Latency of ~1h/1000 km (precedent: Anatahan, Chaiten)

Kasatochi

Summary & Next Steps• ASHE system demonstrated capability to reliably monitor volcanoes at regional distances, with an automatic eruption notification latency of 5 minutes or less for arrays deployed within 40 km. Although sufficiently mature, in the US this technology is not yet integrated into operational environments.

• Global Infrasound Network capable of detecting large eruptions with a latency of ~1h/1000 km. New global study will be initiated by ASHE team in Winter 2008.

• Future research on propagation studies, correlating ash emissions with different type of infrasonic signals, and a more complete understanding of jet noise. Extend existing detection and notification algorithms to other volcanic environments. Evolution and refinement of notification thresholds.

• Recommendations of the 4th Meeting of the International Airways Volcano Watch Operations Group, Paris, France 15-19 September 2008: That VAACs Montreal, Washington and Toulouse a) Continue to assess the feasability of using infrasound data to automatically identify ash producing volcanic eruptions b) prepare a report in time for consideration by the IAVWOPSG-5 Meeting (March 2010).