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Information message about the devastating earthquake in Central Italy, October 26, 2016

The devastating earthquake M=5.3 has occurred on October 26, 2016 at 17:10 GMT (20:10 Moscow time) in Central Italy. 2 hours 8 minutes later - at 19:18 GMT (22:18 Moscow time) there was second shock M=6.2.

Alert message about the first earthquake was issued in 10 minutes after it happened and it was transferred to MOE operational duty of Russia. The message about the second earthquake was transferred after 9 minutes.

Preliminary summary processing of the first earthquake was based on the data of 17 stations, accurate processing - with data of 70 stations. Preliminary summary processing of the second earthquake was based on the data of 14 stations, accurate processing - with data of 79 stations.

Fig. 1 presents fragments of records obtained from digital stations Kaliningrad (∆ 12.6º), Malin Array (∆ 13.5º), Keshkin SH Array (∆ 15.7º), Kongsberg (∆ 16.9º), Anapa (∆ 17.6º) for the second earthquake. Fig. 2 presents fragments of records obtained from digital stations Obninsk(∆ 19.5º), Kislovodsk (∆ 21.4º), Khabaz (∆ 21.6º), Garni (∆ 23.8º), Belogornoye (∆ 24.9º) for the second earthquake.

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:

Note: [1]- data for the first earthquake [2]- data on the second earthquake

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	19-18-06.7	42.93	13.14	10	79	6.2/37	6.2/40	8.5-9	149	IPC GS RAS (Accurate [2])
2	17-10-37.1	42.9	13.16	10	70	5.3/27	5.8/39	7-7.5	149	IPC GS RAS (Accurate [1])
3	17-10-43.6	42.93	13.44	33	17		5.8/9	5.5-6		IPC GS RAS (Preliminary [1])
4	19-18-12.2	43.22	13.69	10	14		6.3/9	8.5-9		IPC GS RAS (Preliminary [2])
5	17-10-36.7	42.88	13.13	9	174	Mw 5.5			26	CSEM ([1])
6	19-18-06.3	42.92	13.12	10	20	Mw 6.1			84	CSEM ([2])
7	17-10-37.9	42.86	13.02	10	624	Mw 5.5	5.6		31	NEIC ([1])
8	19-18-08.3	42.93	13.04	10	185	Mw 6.1	6.1		21	NEIC ([2])

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 presents with red star the epicenter of the first earthquake, its origin was located in the central part of Italy, at a depth of 10 km, 63 km NNW of L'Aquila, 69 km ESE of Perugia and 124 km NE of Rome. Fig.3 presents with yellow star the epicenter of the second earthquake, its origin was located in the central part of Italy, at a depth of 10 km, 3 km NW of the first shock.

Figure 3

Aftershock

GS RAS registered 7 aftershocks M>=4.2 within 13 hours after the second 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
20163812	2016-10-26 21:24:51.0	42.88	13.02	10	14	-	4.2/ 9	3.5	Central Italy
20163807	2016-10-26 21:42:02.0	42.87	13.24	10	30	-	5.1/ 17	5.5-6	Central Italy
20163815	2016-10-26 23:52:30.0	42.96	13.16	10	9	-	4.3/ 7	3.5-4	Central Italy
20163813	2016-10-27 00:21:29.0	43.02	13.13	10	13	-	4.3/ 4	3.5-4	Central Italy
20163810	2016-10-27 03:19:27.0	42.91	13.11	10	19	-	4.6/ 14	4.5	Central Italy
20163811	2016-10-27 03:50:24.0	43	13.13	10	25	-	4.8/ 16	4.5-5	Central Italy
20163817	2016-10-27 08:21:44.0	42.91	13.04	10	12	-	4.6/ 6	4.5	Central Italy

Macroseismic manifestations

According to ITAR-TASS 8 persons were injured after the earthquake. Serious destructions were registered in the settlements Wyss, Ussita, Kastelandzhelo sul Nera, Camerino, Akuasanta Terme, Fabriano. Undeground shocks were felt in Rome, Perugia, Rieti, Norcia, Florence, Bologna and elsewhere in Italy. Fig. 5 was obtained from USGS NEIC, it presents USGS Community Internet Intensity Map for the first earthquake based on 305 responses in 106 cities. Fig. 6 was obtained from USGS NEIC, it presents USGS Community Internet Intensity Map for the second earthquake based on 469 responses in 180 cities.

Figure 4

Figure 5

Historical records

The epicenter of the first earthquake is 20 km away and the epicenter of the second earthquake is 24 km N-N-W of the epicenter of the devastating earthquake of August 24, 2016 М=6.2. At that time 297 persons were killed and Amatrice, Pescara del Tronto, Akkumuli settlements located in a mountainous area were severely affected.

Focal mechanism and seismic moment of the earthquake

Focal mechanism solutions of the origin of this earthquake which occurred on October 26 2016 at 19:18 with М=6.2 were obtained in USGS NEIC with W-phase Moment Tensor (Mww) technique and in HRVD Center, USA (Global CMT Catalog) with СМТ (Centroid moment tensor) technique, these solutions are presented in fig. 6,7, elements of that mechanism are given in table 2. Both solutions are close. The earthquake has occurred under the action of tensile stresses oriented north–east (south-west). Both nodal planes strike north-west-south-east and have declination angle to the horizon DP=40º-53º. The type of motion along both nodal planes – normal fault (in HRVD solution - with insignificant slip component). According to USGS Mo= 1.84* 10** 18 N*m, Mw = 6.1; according to HRVD – Mo= 1.76* 10** 18 N*m, Mw=6.1. The seismic moment of the earthquake was obtained in IPC GS RAS from spectra of Р-wave registered at «Arti» station (Δ 31.7º), Мо=2.3* 10** 18 N*m, Mw = 6.2.

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
5	244	85	78	1	335	333	40	-92	155	50	-89	NEIC
7	65	77	302	11	156	142	40	-107	344	53	-76	HARVARD

NEIC - National Earthquakes Information Center of US Geological Service

HARVARD - Harvard Geophysical Center (USA)

Figure 6

Figure 7