Il-young CHE, Hee-il LEE* Earthquake Research Center

A Study on Characteristics of A Study on Characteristics of Seasonally Dependent Seasonally Dependent

Infrasound Propagation Based Infrasound Propagation Based on the Ground-Truth Events on the Ground-Truth Events

from a Long-Term Experiment from a Long-Term Experiment at a Quarry mineat a Quarry mine

A Study on Characteristics of A Study on Characteristics of Seasonally Dependent Seasonally Dependent

Infrasound Propagation Based Infrasound Propagation Based on the Ground-Truth Events on the Ground-Truth Events

from a Long-Term Experiment from a Long-Term Experiment at a Quarry mineat a Quarry mine

Il-young CHE, Il-young CHE, Hee-il LEE*Hee-il LEE*

Earthquake Research CenterEarthquake Research Center Korea Institute of Geoscience & Mineral Resources(KIGAM), Daejeon, KoreaKorea Institute of Geoscience & Mineral Resources(KIGAM), Daejeon, Korea

Presented at 2008 Infrasound Technology WorkshopPresented at 2008 Infrasound Technology WorkshopBermuda, November 3 – November 7, 2008Bermuda, November 3 – November 7, 2008

With the contribution of Dr. Alexis Le PichonWith the contribution of Dr. Alexis Le Pichon

Korea Institute of Geoscience and Korea Institute of Geoscience and Mineral ResourcesMineral Resources


516 SA events in 2006 649 SA events in 2007

Increase accuracy of localization of the seismo-acoustic events

Motivation

• Total number of 649 seismic events, i.e., 10% of total seismic events, were discriminated as surface explosion by the seismo-acoustic analysis in 2007

• Most seismo-acoustic events are closely gathered in several regions and show similar distribution pattern to previous years

169 Events

Seismic DataSeismic Data

Infrasound

25

194

341

79 10•0

•50

•100

•150

•200

•250

•300

•350

•N

um

bers

~< 0.5 ~<1.0 ~<1.5 ~<2.0 ~<2.5

•Local magnitude (M•L•)

•Seismic magnitude (M•L•) of SA in 2007



Developing accurate locator for small seismo-acoustic events

Assessing detectability of the stations

Characterizing infrasound propagation according to season – arrival time, back-azimuth, attenuation, etc

Deriving experimental relationship between charge size and amplitude from source time function

Objectives



(37.5478N, 128.9614E)

Experiment at a Quarry Mine (2007-2008)

Deployment of 2 Stations - CMT40T-1, Chaparral M2, Q330 Deployment of 2 Stations - CMT40T-1, Chaparral M2, Q330 Operation :Operation : - 1.5 Month Test in 2006 - from Apr. 2007 -

Blasting Information Blasting Information - Everyday at 3h (UTC) - 0.1~10 tons ANFO



Experiment at a Quarry Mine (2007-2008)

Station informationStation information

KSGAR (2003) - 11 elements (4)- Distance : 126.9km- Back-azimuth : 155.2°

CHNAR (1999) - 11 elements (4)- Distance : 180.4km- Back-azimuth : 115.8°

BRDAR (2004) - 13 elements (5)- Distance : 383.0km- Back-azimuth : 95.6°

TJIAR (2002) - 4 elements (1)- Distance : 192.7km- Back-azimuth : 47.2°



Source Time Function (1)

Source signals measured near the blasting point (2007/06/01)Source signals measured near the blasting point (2007/06/01)

- Charge Size : 0.1 t

- Dominant Frequency ~ 2Hz

- P-to-P Amplitude : 39 μbar

- Empirical expression relating acoustic pressure to yield- Calculate source energy- Amplitude attenuation- etc.

Origin Time : 02:55:45.4

Seismic

Infrasound

Air wave



Source Time Function (2)

Source signals measured near the blasting point (2007/06/15)Source signals measured near the blasting point (2007/06/15)

- Charge Size : 8.0 t

- Dominant Frequency ~ 1.8Hz

- P-to-P Amplitude : Clipped

Aseismic ↔ AinfrasoundSeismic

Infrasound

Air wave



Data Analysis

Detection & Parameter EstimationDetection & Parameter Estimation

Phase IdentificationPhase Identification

- KSGAR: mainly - KSGAR: mainly Iw, (Is)Iw, (Is)- CHNAR:- CHNAR: Is Is- BRDAR: - BRDAR: Is, IsIs, ItIs, IsIs, It- TJIAR: - TJIAR: IsIs

Based on our previous experience gained in 2006 – expected time Based on our previous experience gained in 2006 – expected time of arrival to the stations and phases, data was analyzed semi-of arrival to the stations and phases, data was analyzed semi-automaticallyautomatically



Data Analysis by PMCC

Data recorded at CHNAR on 01 June 2007Data recorded at CHNAR on 01 June 2007

Expected arrival time of Is



Speed: 358 m/sAzimuth: 116.8±0.2°


Speed: 352 m/sAzimuth: 116.5±013°





Data Analysis by PMCC (01 June 2007)

Unexpected Problem : many signals coming from the same direction in a limited time window

Back-Azimuth : 115.8 °Back-Azimuth : 115.8 °



Blastings at the nearby mines

Distances in KmDistances in Km(Back Azimuth in Degree(Back Azimuth in Degree))

　 Study MineStudy Mine Mine AMine A Mine BMine B RemarksRemarks

BRDARBRDAR383.0 95.6

391.5 97.0

404.3 97.4

< 2.o°

CHNARCHNAR180.4 115.8

191.4117.6

204.5 117.2

< 2.o°

KSGARKSGAR126.9155.2

139.4154.4

149.4 151.0

< 5.o°

TJIARTJIAR192.7 47.2

191.350.9

198.0 54.2

<7.2°



Seasonal Variation of CelerityExactly measured celerity(Is) from mine to CHNAR

: 0.27 km/s (Apr.) 0.29 km/s (Aug.) 0.27 km/s (Oct.) 0.26 km/s (Jan.) 0.27 km/s (Apr. 2008)

The experiment shows first arrival is close to Is phase, guided wave propagating between the stratopause and the ground.

Celerity is strongly depending on seasonal velocity structure in atmosphere. Seasonal dependency of celerity should be considered in the infrasonic location method

600

620

640

660

680

700

2007

-04-

23

2007

-05-

07

2007

-05-

21

2007

-06-

04

2007

-06-

18

2007

-07-

02

2007

-07-

16

2007

-07-

30

2007

-08-

13

2007

-08-

27

2007

-09-

10

2007

-09-

24

2007

-10-

08

2007

-10-

22

2007

-11-

05

2007

-11-

19

2007

-12-

03

2007

-12-

17

2007

-12-

31

2008

-01-

14

2008

-01-

28

2008

-02-

11

2008

-02-

25

2008

-03-

10

2008

-03-

24

Day

Infr

aso

un

d t

rave

l ti

me

s (

s)

Spring timeSpring time

Summer timeSummer time

Autumn timeAutumn time

Winter timeWinter time

November

Spring timeSpring time



Modelling with ECMWF (in Summer)

2007/06/01_ECMWF91_UVTSPQZ (From mine to CHNAR)TauP & WASP 3D

Z=44.1km, X=192.1/180.4, T=682.04s, Vt=354.55m/s, Vapp=281.65m/s, Daz=0.31°Z=43.5km, X=199.5/180.4, T=702.95s, Vt=351.55m/s, Vapp=283.80m/s, Daz=0.35°

We thank IDC for providing the ECMWF91 data and Dr. Alexis for doing ray-tracing with them.

Slowness

Wind correctedSlowness



Modelling with ECMWF (in Winter)

2007/12/22_ECMWF91_UVTSPQZ (From mine to CHNAR)TauP & WASP 3D

Z=0.2km, No=36, X=182.1/180.4, T=540.68s, Vt=339.13m/s, Vapp=336.77m/s, Daz=-0.53°Z=0.2km, No=35, X=177.0/180.4, T=525.66s, Vt=339.13m/s, Vapp=336.77m/s, Daz=-0.53°Z=0.2km, No=37, X=187.1/180.4, T=555.70s, Vt=339.13m/s, Vapp=336.77m/s, Daz=-0.53°

Slowness

Wind correctedSlowness



Why detectability is increasing in Summer?

The experiment also shows detectability in summertime is higher than autumn-winter-spring seasons.It implies that infrasound propagation and detection are related with seasonal wind in and around the Korean Peninsula. We interpret that lower detectability in autumn-winter-spring is due to prevailing NW wind, its direction is opposite to infrasound propagation from the mine to CHNAR.

Detected

Not detected

Observed up to 30km at SokchoObservatory (47090)



Surface Winds Affects the Detectability?

The wind speed and direction are value averaged over 1 minute window at the time of blasting

Detectability

CHNAR : ~55% (in Summer) ~40% (all over the season)

KSGAR : less than 5%

At least one station : ~ 40%Two stations : ~16%Three stations : ~10%Four stations : < 5%

Do surface wind fields near the source affect the detectability? No!Do surface wind fields near the source affect the detectability? No!



Localization by SALoc

Seismo-acoustic location method

Location method for small-magnitude surface explosions - generating both seismic and infrasonic signals

Grid search method - finding a location where the time residual between observed and model predicted is minimum at the grid points with initial conditions : origin time, celerity, wind-corrected back-azimuth

An example : location results for 6 tons of ripple-firing shot

,



Comparison of localization results

Comparison of localization results for 21 ground-truth events

The seismo-acoustic location shows a mean location error of 5.7 km, which represents a substantial improvement in location accuracy of 58.7% and 46.7% compared to the seismic location and infrasonic-azimuth intersection methods, respectively.



Summary & General Remarks

Detectabilty is increasing in Summer

Long-term measurement over the years will be helpful to clarify seasonal variation of celerity and to study atmospheric effects on infrasound propagation in mid-latitude Northern Hemisphere around the Korean Peninula

Celerity (Is) between CHNAR and mine changes as follows;- 0.27 km/s in April 2007

- 0.29 km/s in August 2007- 0.27 km/s in October 2007- 0.26 km/s in January 2008- 0.27 km/s in April 2008

Most frequently detected phase is Is at the stations of interest



Summary & General Remarks

SALoc significantly reduces location error for small magnitude explosion, M < 2.0



In the Future

Recovering source waveform saturated

Empirical relationship between the amplitude of the source wavelet/energy/measured amplitude

Continue this experiment to the next April to see seasonal change is consistent from year to year

Il-young CHE, Hee-il LEE* Earthquake Research Center

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