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Information message about the strong earthquake in the region of Crete, Greece, April 16, 2015

The strong earthquake M=6.2 has occurred on April 16, 2015 at 18:07 GMT (21:07 Moscow time) in the region of Crete, Greece.

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 1 ч 30 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 33 stations, accurate processing - with data 64 stations.

Fig. 1 presents fragments of records obtained from digital stations Apeiranthos of Naxos (∆ 2º), Keskin Array (∆ 7º), Kislovodsk (∆ 15º), Garni (∆ 15º), Khabaz (∆ 15º). Fig. 2 presents fragments of records obtained from digital stations Kasperske Hory (∆ 16.9º), Obninsk (∆ 21º), Belogornoye (∆ 22.7º), Kirov (∆ 27.7º), Arti (∆ 30.2º).

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	18-07-42.5	35.28	26.74	25	64	6/27	6.2/30	7-7.5	140	IPC GS RAS (Accurate)
2	18-07-46.7	35.4	26.9	33	33		6.2/26	7-7.5	140	IPC GS RAS (Preliminary)
3	18-07-43.8	35.02	26.81	25	631	Mw 6.1			31	CSEM
4	18-07-42.9	35.14	26.82	20	755	Mw 6			25	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 presents with red star epicenter of this earthquake, its origin was located in the Mediterranean Sea near the coast of Crete Island, Greece, at a depth of 25 km, 45 km E of Palaikastron, 147 km E of Iraklion and 185 km S-W of Rodhos.

Figure 3

Aftershock

GS RAS registered 3 aftershocks Рњ>=5.2 within 8 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
20151294	2015-04-16 18:52:35.0	35.08	26.83	25	37	-	5.2/ 15	4.5	Crete, Greece
20151295	2015-04-16 19:02:14.0	35.11	26.79	33	43	-	5.2/ 19	4-4.5	Crete, Greece
20151300	2015-04-17 02:05:37.0	35.05	26.64	10	46	-	5.5/ 21	6.5-7	Crete, Greece

Macroseismic manifestations

Fig. 4 was obtained from USGS NEIC , it presents USGS Community Interenet Intensity Map based on 19 responses in 14 cities.

Figure 4

Historical records

The last strong earthquake in this region was registered on April 1, 2011 M=6.5 67 km to the North.

Focal mechanism and seismic moment of the earthquake

Focal mechanism solution was obtained in IPC GS RAS with signs of initial arrivals of P waves at 69 stations, including 45 stations which registered compression waves (plus sign) and 24 stations which registered tensile waves (minus sign). All stations are located in the interval of epicentral distances of 1вЂ“97º with azymuthal sector Az=1-358º. Focal mechanism solution in stereographic projection at the lower hemisphere is presented at fig. 5, elements of mechanism are presented in table 2. Fig. 6, 7 present focal mechanism solutions obtained in USGS NEIC with W-phase Moment Tensor (Mww) technique and in Quick CMT Center obtained with CMT technique. Elements of these mechanisms are also presented in table 2. All solutions obtained in different centers are almost identical. The motion has occurred under the action of compression stresses oriented to the North. Nodal plane 1 strikes N-W (STK=292-306º), nodal plane 2 strikes N-E (STK= 48-58º). Both nodal planes decline to the horizon under nearly equal angles (PL=50-66º). The type of motion along both planes is characterized as slip with thrust fault component: NP1 вЂ“ right lateral slip, РїРѕ NP2 вЂ“ left lateral slip. Seismic moment was obtained in IPC GS RAS with spectra of Р waves registered at station В«TalayaВ» (∆55.6º), Mo=1.8*10**18 N*m, Mw=6.1. According to USGS NEIC вЂ“ Mo=1.456*10**18 N*m, Mw=6.0, according to CMT вЂ“ РњРѕ=1.72*10**18 N*m, Mw=6.0.

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
48	265	10	5	41	104	306	66	135	58	50	32	IPC GS RAS
48	258	0	348	42	79	292	58	141	45	58	38	NEIC
44	261	5	356	45	91	300	64	142	48	56	31	Quick CMT

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

NEIC - National Earthquakes Information Center of US Geological Service

Quick CMT - Quick CMT catalog

Figure 5	Figure 6

Figure 7