Report on April 6th
Central Italy(L'Aquila)Earthquake |
Launched: April 7, 2009
Last Updated:
April 18, 2009 |
At 10:32am (JST; 3:32am local time), April 6th, 2009, a Mw 6.3 ( by Global CMT project) earthquake occurred at L’Aquila,
a central city in Italy (lat=45 N, lon= 13.33 E, depth=8.8km). It has resulted in a severe damage due to the shallow
inland earthquake.
294 people has been reported dead, 55,000 injured and 1,500 as refugees
as of April 13th (local
time). A joint funeral took place on Friday, the 10th. In addition, a M 5.5 aftershock occurred on April 8th at 2:47am (Japan time) and it now has the prospect of this earthquake
becoming one of the swarm activity.
We will update information on this earthquake. (Outreach Office)
[Updated]
[Tectonics Background]
The Eurasian Plate and the African Plate collides beneath the Mediterranean
Sea and its rock mass subducts from eastern Italy towards southern Italy.
(The deep earthquake within the black dotted circle occurred due to this
subduction.) On the other hand, the basin at the Tyrrhenian Sea is spreading
and it can be said that this area is a tensional stress field.
Since this earthquake has a different fault strike (NW- SE) from the collision
direction of the Eurasian/African Plate (N-S), it can be stated that this
earthquake has been contributed by the tensional stress field around the
Tyrrhenian Sea rather than the compressive stress field caused by both
of the plates.
Blue line： Eurasian/ African Boundary drawn referring to the PB2002
Dots： Earthquakes occurred during 1977〜March 25th, 2009
★： Central Italy (L`Auila ) earthquake
[References]
- PB2002: Plate Boundary Model（by Peter Bird, UCLA）
- Boncio & Lavecchia, Journal of Seismology, 2000
- Cello et al., Journal of Seismology, 2000
- Morelli et al., Journal of Seismology, 2000
- Salvi et al., Geophys. J. Int. 2003
[Source Process Inversion]
click the figure to link
Natalia Poiata （D2）
[Source Mechanism by W-phase（Preliminary Result）]
Mw = 6.14
Fault Surface 1： Strike, Dip, Slip : 315.7 / 54.6 / -97.3
Fault Surface 2： Strike, Dip, Slip : 148.2 / 36.0 / -79.9
Reference：
Source Mechanism by Global CMT Project ( Goran Ekstrom, Columbia University)
 (click the figure to link)
Other source mechanism solutions：
USGS： Scientific & Technical Information
Yusuke YOKOTA（M2）
[Foreshock Activities]
Remarkable foreshock activities were to be seen before this earthquake.
According to the data by the INGV ( Istituto Nazionale di Geofisica e Vulcanologia)
of Italy, this area was a place where small earthquakes occurred a few
times monthly. The number of small earthquakes gradually increased from
the beginning of this March to as many as 9 small moderate-sized earthquakes
(the largest is M4.0 ) on March 30th. There were then 2-4 foreshocks everyday (largest is M4.6 ) before the
main shock at 1:32PM, April 6th. It is easily presumed
that there would have been a high possibility of panic had there been any prediction information from
the public.
Prof. Kazuki KOKETSU
[Waveforms observed by J-array]
Earthquake Information Center
[Past damaging earthquakes in this region：from USGS website]
A Mw6.0 earthquake has happened in Umbria-Marche, 85km NNW of this earthquake.
Death toll was 11, more than 100 injuries and 80,000 household destructions.
This 1997 earthquake is known as one of the swarm activities which eight
earthquakes over M5.0 happened within two months.
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