infrasonic measurements of the carancas, peru meteorite fall p. brown 1, w.n. edwards 1, a. le...

Infrasonic Measurements of the Carancas, Peru Meteorite Fall

P. Brown1, W.N. Edwards1, A. Le Pichon2, K. Antier2, D.O. ReVelle 3, G. Tancredi4, S. Arrowsmith 3

1Dept. of Physics and Astronomy, U. of Western Ontario, London, ON, Canada N6A 3K7

2Commissariat à l’Energie Atomique, Centre DAM - Ile de France, Département Analyse Surveillance Environnement, Bruyères-le-Châtel, 91297 Arpajon

Cedex, France

3EES-17, Geophysics Group – Earth and Environmental Science Division, Los Alamos National Laboratory, P.O. Box 1663, MS D401, Los Alamos, NM 87545

USA

4Dpto. Astronomía, Fac. Ciencias, Iguá 4225, 11400 Montevideo, Uruguay.

Infrasound Technology Workshop - 2008

What happened?• 15/9/2007 – ~ 11:45 LT (16:45 UT) a bright fireball was

observed in the sky near the Peru/Bolivia border, leaving behind a smoke trail. Strong explosions lasting several seconds were heard in an area of several tens of km.

• A ground-level explosion was observed as well as the formation of a thick cloud of dust like a mushroom cloud.

• The shock wave of the ground level explosion produced vibration in several houses and some animals were knocked down due to the shock wave. The roof of a shed was impacted by ejecta.

• At the site where the explosion and the dust cloud was observed, the local people found a ~14m crater. The crater was half-fill by underground water. The water was bubbling and noxious fumes were coming out the water.

• Several pieces of atypical material was collected from inside and outside the crater.

• Several persons got sick.

Photo of the smoke trail

Crater: diameter 14m

Carancas crater

Carancas meteorites

Photo José Ishitsuka

Photo Hernando Nuñez

Puzzles presented by this event• What happened to the original meteorite?

Was it fragmented and totally dispersed during the impact?

• How was it possible that a chondritic meteorite of just a few meters in size could get through the atmosphere without being completely disrupted?

• Under what conditions could this event happen again?

From Bland and Artemieva (2003)

This figure portrays the ratio of final mass to initialmass for stoney meteorites (top) and irons (bottom)

From Hills and Goda (1998)

Constraints on the explosion energyThe explosion produced by the impact of the meteorite with the

ground was witnessed by several people. The explosion created an expanding cloud of dust and debris and a shock wave.

Local blast constraints:• A man standing ~400m from the crater site saw the expanding

dust cloud, heard the explosion but did not suffer any injury, nor did he fall down.

• A man riding a bicycle ~100m from the crater fell down and he felt a bit dizzy due to the explosion, but his eardrums were not ruptured. He was riding in a direction orthogonal to the line connecting to the crater.

• A bull similar to the Lidia bull-fighting breed was at ~200m from the crater. It fell down and broke one of its horns. The bull weighed ~500 kg.

• A mud shed with metal roof at ~120m was not seriously damaged. The shed has no glass windows. It was hit by ejecta from the crater that bent a metal sheet of the roof.

Pressures for1 & 3 ton TNT

Cratering Energetics from Holsapple and Housen (2007)

Cratering Energetics from Holsapple and Housen (2007)

Available Instrumental Data

• Infrasound:– IS08 (Bolivia): Two strong airwave arrivals

associated with the event (80.3 km range)– IS41PY (Paraguay): Very weak signal (1663 km

range)

• Seismic:– Bolivian Short-period seismic stations (BBOD,

BBOE, BBOK, BBOB)• Detect impact directly (Pg waves) and airwave

arrivals

– LPAZ (Bolivia): Pg arrival (106 km)

Time from 16 40 UT

Am

plitude (nm)

Am

plitude (Pa)

1 2

Arrival Angle ~ 14°Arrival Azimuth ~ 228 °

Arrival Angle ~ 19°Arrival Azimuth ~ 215 °

Bp 0.3 – 8 Hz

Zonal Wind Speed (m/s)-40 -20 0 20 40

Hei

ght (

km)

0

20

40

60

80

100

Meridional (m/s)

-40 -20 0 20 40

Hei

ght (

km)

0

20

40

60

80

100

Atmosphere

Pg waves from Crater Formation

16 40 00 UT +

Dis

plac

emen

t (n

m)

Crater formation time = 16 40 14.5 ± 0.4 UTPg wave velocity = 5.1 ± 0.1 km/s

Trajectory• Possible Trajectory hypotheses to explain double signal:

1. Airshock from ballistic arrival and airwave from crater production

2. Airshock from ballistic arrival and fragmentation event

3. Double fragmentation events

• Additional constraining data for fireball direction:

1. South of IS08

2. Consistent with eyewitnesses near crater describing E->W path

3. Crater ejecta concentrated to SW and SSW

Trajectory azimuth confined to ~easterly radiant azimuths

Quasi - Ballistic Wave Model• Use timing for crater

formation as constraint and minimize residuals from line source– Free parameters are

azimuth and altitude of radiant and velocity

• Allow ray deviations up to ~20° from perpendicular

NO

N-B

AL

LIS

TIC

NO

N-B

AL

LIS

TIC

NO

N-B

AL

LIS

TIC

NO

N-B

AL

LIS

TIC

QUASI-BALLISTIC

QUASI-BALLISTIC

QUASI-BALLISTIC

QUASI-BALLISTIC

BA

LL

IST

ICB

AL

LIS

TIC

V

Quasi - Ballistic Wave - Solutions• Assuming first arrival from IS08 is

associated with crater formation AND is associated with major arrival at other stations get celerities from 0.31 – 0.33 km/s clustered around 0.33 km/s (plausible)

• Second arrival at IS08 and secondary arrivals at seismic stations are taken to be ballistic arrival

• Solutions have possible azimuths from 75 – 125 and steep elevations (>60 degs)

Point Source Solutions• Several arrival combinations possible –

associations uncertain• Main Result – Point source solutions for all

combinations cluster from 80 -110° az and entry angles from 32° – 60° with heights clustering at 20 ± 3 km and 30 ± 2 km for all solutions

• Best fit presuming both main arrivals are fragmentation related and forced to fit IS08 backazimuths is az ~ 90° and 35° elevation

Rad

ian

t A

zim

uth

Entry Angle Entry Angle

IS08 2nd arrival azimuth fit with 1st arrival crater airwave

Line Source Model – differing signal picks

From Le Pichon et al (2008)

Crater Energetics – IS08

• From airwave at IS08 can apply empirical yield relations to estimate source energy (presuming first airwave arrival at IS08 is from crater or very late stage fragmentation event)

– Davidson and Whitaker (1992): Es = 4.5 tons TNT

96.4log2log47.1log RPE cSAP hkv

c 10

Signal Property Wavetrain #1 Wavetrain #2

Zero – Peak Amplitude (Pa) 0.76 ± 0.21 0.59 ± 0.14

Peak-Peak Amplitude (Pa) 1.91 ± 0.51 1.19 ± 0.25

Period at Max Amplitude (sec) 0.52 ± 0.03 0.62 ± 0.20

Summary of IS08 airwave arrival data:

• Airwave data from I41PY:

• Energy Estimations:

Crater Energetics – I41PYSignal Property Value

Zero – Peak Amplitude (Pa) 0.03 ± 0.01

Peak-Peak Amplitude (Pa) 0.04 ± 0.02

Period at Max Amplitude (sec) 1.2 ± 0.2

58.2log34.32log

PES

62.10log52.3log2log RPES

bb

kva

S AREh 3

33

10

Source Relation Energy (tons of TNT)

ReVelle (1997) ; US Nuclear TestsAFTAC (period at max amplitude)

Blanc et al (1997) ; French Nuclear Tests (amplitude + range)

Edwards et al (2006) ; Comparison of bolide infrasound and satellite data(amplitude, winds and range)

10 ± 5

4 ± 3

5 ± 2

Seismic Energies/Efficiencies

• From seismic arrivals, the crater explosion produced an equivalent local seismic magnitude ~ ML = 1.3 ± 0.1

• Corresponds to seismic energy of ~106 J

• Event energy ~3 tons TNT ~1010 J

• Seismic efficiency ~10-4

• Shishkin (2007) theory predicts ~10-5 to 10-6

Modelling• Entry modelling (two

separate models)• Orbital solutions limit initial

v < 17 km/s to have aphelia inside Jupiters orbit

• Assumption is no major fragmentation Height (km)

10 20 30 40 50 60

Mas

s (k

g)

2000

3000

4000

5000

6000

7000

8000

9000

10000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Vo=12km/s, = 0.004Vo=17km/s, = 0.008Vo=12km/s, = 0.004Vo=17kms, 0.004

Height (km)0 10 20 30 40 50

Vel

ocit

y (k

m/s

)

0123456789

101112131415161718

Summary : Conclusions• Initial mass of meteoroid 4 000 – 12 000 kg

– Initial radius is 0.6 – 1 m

– Most probable near lower end of range

• Initial velocity 12 – 17 km/s– Initial energy ~0.1 – 0.4 kT TNT

• Impacting velocity @ ground ~1.5 – 4 km/s (model dependent); PDFs suggest 3-6 km/s

• Impactor mass at ground 2 000 – 5 000 kg (model dependent)

• Impact energy ~a few tons TNT • Seismic Impact Efficiency ~10-4

Working Hypothesis• The Carancas meteoroid was unusually strong, with

few stress cracks (Y ~ 15 MPa)

• It did not fragment significantly and therefore did not loose all of its pre-encounter cosmic velocity (having a ~few percent of its pre-encounter KE upon impact).

• Models based on average properties miss important details

“The enemy of the conventional wisdom is not ideas but the march of events” – J. K. Galbraith