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Information message about destructive earthquake in central Italy on April 6, 2009

The earthquake with М=6.4 has occurred on April 6, 2009 at 01:32 GMT (05:32 Moscow time) in central Italy. It caused victims and destructions.

Parameters of the earthquake have been determined in the Alert Service (AS) of Information Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad. Alert message on this earthquake has been delivered in 32 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 47 stations, accurate processing - with data 53 stations.

Fig. 1 presents fragments of records obtained from digital stations Kasperske Hory (∆ 6.6º), Apeiranthos (∆ 6.8º), Kiev (∆ 13.6º), Obninsk (∆ 19.7º), Pulkovo (∆ 20.2º), Kislovodsk (∆ 21.3º). Fig. 2 presents fragments of records obtained from digital stations Lovozero (∆ 27.9º), Arti (∆ 31.8º), Kingsbay (∆ 36.5º), Borovoe (∆ 38.7º), Ala Archa (∆ 44.1º), Kurchatov (∆ 44.2º).

Figure 1

Figure 2

IPC GS RAS also has obtained information with parameters of this event from some seismological centers, these data are given in table 1:

Table 1

NN	Time in origin h-min-s (GMT)	Lat degr.	Lon degr.	Depth km	N s/st	Ms/ N	mb/ N	I0 calc	GAP	Center
1	01-32-41.1	42.51	13.4	10	53	6.4/15	6.2/29	9-9.5	155	IPC GS RAS (Accurate)
2	01-32-41.3	42.52	13.43	10	47	6.4/15	6.3/20	9-9.5	174	IPC GS RAS (Preliminary)
3	01-32-41.1	42.51	13.4	10	53	6.4/15	6.2/29	9-9.5	155	IPC GS RAS (Accurate)
4	01-32-41.3	42.52	13.43	10	47	6.4/15	6.3/20	9-9.5	174	IPC GS RAS (Preliminary)
5	01-32-41.4	42.38	13.32	2	669	6.3 Mw			9	CSEM
6	01-32-41.4	42.38	13.32	2	669	6.3 Mw			9	CSEM
7	01-32-42.4	42.42	13.4	10	66	6.3 Mw	6.0/24		50	NEIC
8	01-32-42.4	42.42	13.4	10	66	6.3 Mw	6.0/24		50	NEIC

IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences

CSEM - European - Mediterranean seismological center

NEIC - National Earthquakes Information Center of US Geological Service

Epicenter

Fig.3 depicts with yellow star epicenter of this earthquake, which was located in central part of Italy at the depth of 10 km, this is 17 km north from Aquila, 103 km N-E from Rome and 108 km S-E from Perugia.

Figure 3

Aftershock

GS RAS has registered: 1 foreshock with М=4.5 (5 before the main shock)and 4 aftershocks with М>4.5 (within 6 hours after the main shock).

N	Date & Time (GMT) yy-mm-dd hh:mm:sec	Lat degr.	Lon degr.	Depth km	N station	Ms/ N	mb/ N	Io calc.	Region
20091163	2009-04-05 20:48:55.0	42.51	13.41	10	11	-	4.5/ 7	4-4.5	Central Italy
20091166	2009-04-06 02:27:47.0	42.49	13.31	10	9	-	4.6/ 6	4.5	Central Italy
20091167	2009-04-06 02:37:04.0	42.46	13.17	10	19	-	5.1/ 11	5.5-6	Central Italy
20091168	2009-04-06 03:56:47.0	42.63	13.51	10	18	-	4.9/ 12	5-5.5	Central Italy
20091172	2009-04-06 07:17:11.0	42.52	13.34	10	14	-	4.7/ 10	4.5-5	Central Italy

Macroseismic manifestations

In accordance with ITAR-TASS agency the number of victims from this powerful earthquake in central part of Italy has reached 40 people. Italian agency ANSA reports about this with reference to information from hospitals of Aquila town, which is administrative center of Abrucci Region, where the underground shocks have occurred. Civil Defense reports that there five children among the killed persons. Moreover 30 people are considered as lost. In the disaster area around Aquila town, which is administrative center of Abrucci Region, nearly 50 percent of the buildings were destroyed including student's campus and the top part of the town's temple. The rescue works continue to find the injured people under the debris. Telephone line is not working and in some places there is no electricity power supply. Underground shocks were felt in the most towns of the country's central part, including the Rome. National emergency was announced in Italy after this earthquake. Fig. 4, downloaded from NEIC USA presents the map with intensities obtained from phone calls of 436 people living in 119 places.

Figure 4

Focal mechanism and seismic moment of the earthquake

Focal mechanism solutions of this earthquake were obtained with TMC technique in NEIC USA, USGS and HRVD USA (Global CMT Catalog), they are presented in table 2 and shown on fig. 5,6. These solutions are close. The earthquake has occurred under the action of N-E oriented expansion forces. Both nodal planes have N-W-S-E direction of propagation and fall rather steeply (falling angles of these planes change in the interval DP=43º-55º). The type of motion along both nodal planes – fault (with components of right side drift along NP1 and left side drift along NP2). The value of seismic moment Мо obtained in IPC GS RAS from Р-wave spectra recorded at four stations: Obninsk (Δ 19.7º), Kislovodsk (Δ 21.3º), Arti (Δ 31.9º), Talaya (Δ 58.4º) makes Мо=4.3* 10** 18 n*m, the value of moment magnitude calculated from Kanamori formula makes Mw = 6.4. the value of seismic moment Мо of this earthquake in accordance with USGS makes 2.9* 10** 18 n*m, the value of moment magnitude makes Mw = 6.2; and in accordance with HRVD – Mo= 3.4* 10** 18 n*m, Mw=6.3.

Table 2

Axes of main strengths						Nodal planes						Center
T		P		N		NP1			NP2
Pl	Azm	Pl	Azm	Pl	Azm	Stk	Dp	Slip	Stk	Dp	Slip
6	54	66	309	22	147	121	43	-122	343	55	-61	NEIC
6	54	66	309	22	147	121	43	-122	343	55	-61	NEIC
3	231	75	334	15	140	127	50	-109	336	43	-68	HARVARD
3	231	75	334	15	140	127	50	-109	336	43	-68	HARVARD

NEIC - National Earthquakes Information Center of US Geological Service

HARVARD - Harvard Geophysical Center (USA)

Figure 5

Figure 6