Civil applications of Infrasound and Seismic Data: Location of the plane crash of Air Algeria.

Disclaimer: The views expressed herein are those of the authors and do not necessarily reflect the views of the CTBTO Preparatory Commission.

NDC BURKINA FASO

S. Emile TIENDREBEOGOb, Pierrick MIALLEa, Oumar SANOGOb,a CTBTO /IDC/SA/SM,Vienna, AUSTRIA

b CNRST, Ouagadougou, BURKINA FASO Corresponding author: t.emile@cnrst.bf

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On 24 July 2014, a civilian aircraft AH5017 from airline Air Algeria, took off from the international airport of Ouagadougou at 00h55mn GMT with 118 passengers on board. Its destination was Algiers international airport in Algeria. One hour later, the flight AH5017 ceased all communications with the control tower in Ouagadougou and that of Niger.

Niger authorities had just taken over the communications with the aircraft a few minutes earlier after being redirected to avoid a big storm over Mali and Southern Algeria. Multiple press releases report that the AH5017 flight disappeared from the radar after being re-routed. It later appeared that the plane crashed shortly after losing contact (Sources: AFP, BBC, Ouagadougou airport, and others).

Our NDC collaborated with IDC staff using IMS infrasound and IDC bulletins on the search for infrasound and seismic signals related to the crash and to locate the crash site.

DATA USED AND INTERPRETATION

I17CI Infrasound propagation status on July 24th 2014

The location is slightly to the east of the reported crash area as TORD detections likely pull the location towards its location (due to large uncertainties on infrasound travel times). However both seismic and infrasound azimuths cross at the crash area.From these findings it seems likely that the seismo-acoustic source observed by the IMS network corresponds to the crash of the AH5017 plane.

This study demonstrates that CTBTO data and products are useful for civilian applications.

IMS SEISMIC AND INFRASOUND NETWORKIn the region around northern Mali the closest certified stations is TORD (Niger, at 360km), DBIC (Côte d’Ivoire, at 720km) and within 2000km is I17CI (Dimbokro, Côte d’Ivoire).

Other regional stations are all located well beyond 2000km in Cape Verde (I11CV), Ascension Island (I50GB) and Tunisia (I48TN)

IDC automatic bulletin reviewLooking into the IDC automatic bulletins (SEL3), no matching event is reported for the region at the approximate time of the crash. The detection bulletins for the 6 closest stations only provide one possible association originating from the explosion site . This detection was made with data from I17CI (Ivory Coast) that is located just over 1000km from the reported crash site.

Infrasound tool s has been used to search for event matching arrivals in IDC bulletins. The source is located in 80km south of Gossi and about 50km from the Burkina Faso border as reported in the press (extending the search to the region around the city) at 01:47GMT (plus or minus 30mn to account for various reported time of explosion) and the receivers are all stations within 40 degrees.All other stations, within 60 degrees, do not exhibit automatic detection in IDC bulletins.

Infrasound threshold monitoring results with DTK-Netperf for Wednesday 23 July at 00:00GMT (Results are unavailable at the time of the crash, but the local network detections appear similar at night-time the previous days)

ECMWF effective sound speed in stratosphere (50km altitude) for Thursday 24 July at 00:00GMT

Geotool-PMCC results for I17CI station between 02:38 and 02:48 on 24 July 2014. The detections emerging from the background noise and clearly identified by PMCC (red) are 3 arrivals likely related to AH5017 crash.

Seismic review : TORD data

Based on infrasound findings and estimated time of theexplosion (including the origin time uncertainties), asearch for associated seismic signals is performed forthe regional stations. On the ground (or close to theground) explosions can generate seismic signal underfavorable conditions, as it can be observed for mining inopen pits or for the 2 infrasound calibration campaignfrom 2009 and 2011 (seismic signals was found forstations within 3 degrees).The data from TORD (Niger, at 360km) and DBIC (IvoryCoast, at 720km) are analyzed primarily, even thoughboth stations appears to be relatively far for theapparent strength of the source. This tends to indicatethat seismo-acoustic coupling occurred and theobserved event took place on the ground (or close tothe ground).

ARS screenshot with Pg and Lg phases on TORD seismic array

LEB event saved with TORD and I17CI detections

Crash LocationBased on TORD and I17CI detections a location can be estimated for the event (Figure 9). The time and location of the event appears to be consistent with the crash of the AH5017 plane reported in northern Mali.

Regional map centered on Burkina Faso. I17CI is displayed in green, and the green line is for its detecting azimuth. TORD is displayed in Orange, with orange lines for both Pg and Lgazimuth.

Conclusion

Summary

T1,5-P7