Earthquakes in Italy

1
Earthquakes in Italy

• Earthquake of the week
  2009 Fall

• Kate Huihsuan Chen 2009/12/21

2
2009 April Mw 6.3 earthquake

• 2009/4/6 132 UTC, 332 local time
• Central Italy
• Devastating the LAquila town and surrounding
  villages of the Abruzzi region
• 297 deaths 1000 injured 66,000 homeless

extension
Chiarabba et al., GRL, 2009
3
Space-time evolution of seismicity

• Which provides accurate earthquake locations and
  the geometry of faults that accommodate the
  extension in this portion of the Apennines.
• Until May 15, more than 6,000 aftershocks were
  located by the surveillance duty.

The date of the most recent historical events
The April 6th, 2009 main shock was preceded by a
long sequence of foreshocks, which started
several months before, culminating with a ML4.1
shock on March 30.
Chiarabba et al., GRL, 2009
4
The main shock rupture activated a NWSE
trending, 1518 km long fault.

• In the first three days after the main event, we
  note a migration of seismicity from the main
  structure northward, culminated with a Mw5.4
  aftershock on April 9th.
• In the following week, seismicity continues
  migrating, spreading from the main fault plane to
  an adjacent laterally offset, normal fault
  located to the north, and toward the southern
  termination of the main fault

Chiarabba et al., GRL, 2009
5
Decay of aftershock

• During the following month, seismicity spread
  along a 40 km long fault system, showing an
  Omori-like temporal decay

Chiarabba et al., GRL, 2009
6
Aftershock distribution induced fault geometry (I)

• The aftershocks clearly define an 1518 km long,
  NW-trending and 45SW-dipping fault, located above
  10 depth, with a seismicity cut-off at 2 km depth
  (sez-2).

a
a
The main shock hypocenter is located at the base
of the aftershocks and close to the northwestern
border of the fault.
(1)
b
b
a
b
c
c
c
a
b
c
Chiarabba et al., GRL, 2009
7
Aftershock distribution induced fault geometry
(II)
(2)
The second large event is the MW 5.6 April 7
(1747) shock that occurred a few kilometers to
the south of the main event, at a depth of 15 km.
Only a few aftershocks followed this event, and
they are located around the ruptured patch
(sez-3). The geometry of this fault, barely
illuminated by aftershocks, is still uncertain
since the shallower earthquakes located above the
hypocenter occur on the fault plane of the Mw6.3
event, with 5 km gap in between.
Chiarabba et al., GRL, 2009
8
Aftershock distribution induced fault geometry
(III)
a

• A third large event is the Mw 5.4, 9th of April
  shock that is located on a fault offset from the
  main plane by a few kilometers northward. Focal
  mechanisms show a pure normal solution.
• The hypocenter is at about 11 km depth and its
  aftershocks define a steep SW-dipping plane
  (sez-1).
• Differently from the April 6 main shock, there
  are no events in the top 6 km of the fault,
  although its upper continuation is consistent
  with the surface trace of the Laga Mts. Fault.

a
Chiarabba et al., GRL, 2009
9
The seismicity cutoff at 2 km depth suggests that
the upper portion of the fault did not slip much,
in agreement with the limited extent of surface
breaks mapped by geologists. In the southern
portion of the fault, the seismicity distribution
is cloudy (sez-3), suggesting a change in the
fault plane orientation along strike or, more
likely, the transition to a more distributed
deformation on several small faults.
Red dots are the ML 4.0 earthquakes. The 1703
and the 1915 earthquakes occurred at the north
and southern border of the Paganica fault.
Chiarabba et al., GRL, 2009
10
Discussion

• The aftershock data suggest a size of 10x6 km2
  for the main ruptured patch, whereas the second
  shallower patch is smaller, 5x5 km2. The third
  patch is smaller and located northward of the
  first two.

Whether or not subsequent large shocks should be
expected?
The catalogue of historical earthquakes reports
several multiple events in the Apennines, with
elapsed times between events spanning from hours
to a few years.
The absence of seismic release in the upper 67
kilometers on the northern segment could be an
indication for a future large shock. However,
this area experienced a large earthquake in 1703
and frequent microseismicity in the last 30 years
that probably decrease the seismic potential.
Chiarabba et al., GRL, 2009
11
This earthquake emphasizes the difficulties of
assessing seismic hazard in regions where there
are many closely spaced faults
12
In addition, analysis of geomorphology using
satellite imagery gives a strike in the range
140145, strongly supporting the strike inferred
by our InSAR model.
13
Seismic hazard assessment

• Static stress calculations show that the
  earthquake has imparted stress changes on other
  nearby active faults, bringing several of them,
  most notably the Montereale and Campotosto
  faults, closer to failure.
• The seismic strain deficit in this area was only
  partially alleviated by the 2009 LAquila
  earthquake sequence and continues to represent a
  seismic hazard in the region.

14
Something about InSAR
15
Surface deformation
16
Surface deformation from SAR
???? ??????????? ??? ??? ???? ?????
17
SAR InSAR D-InSAR

• SAR?
• -?????, ???????,????????? ??? ?????
• InSAR?
• -Interferometric In SAR, ????????????????????,????
  ??????
• D-InSAR?
• -D-InSAR, ????InSAR ? ???????????,???????????????,
  ???????

18
SAR

• ??????,?????????,( ???????????,????????????)
• ???????????????,??????,??,???????????

L-band 20 cm R 600 km Ra 100m Required D
?
??? ?????????????????
19
??????
20
InSAR

• InSAR ?????????????????
• Interferometric SAR, ?????????????????????,???????
  ???????.

21
?????????

• ??????(??SAR?????????)
• ??????????
• ??????
• ????
• ?????

22
D-InSAR????
99/10/28
99/7/15
99/6/10
??
??
????
????
??????1 (Topography)
??????2 (Topography Deformation)
???????
??????
????
????????
23
?????????
???
???
???
???
???
???
24
?????? 2-pass D-InSAR
25
?????? 3-pass D-InSAR
26
????????(4-pass D-InSAR)
27
?GPS?????
9/23-5/6-10/28 D-InSAR result
Displacement field
28
? Model??

• RNGCHN program
• (from Okadas dislocation model, 1985)
• Assumption
• -Earths surface is flat
• -Elastic half-space
• -Isotropic medium
• -?µ1

29

• Interferogram of the central Taiwan area
  (1999/5/61999/10/28 year/month/day).
• Unwrapped result of interferogram. The amount of
  displacement is evaluated in slant range
  direction.

30

• To simulate the interferogram of the C-band radar
  image, we projected each GPS displacement vector
  onto the slant range direction.
• The GPS data used in this study were collected
  from several campaigns mainly conducted by (1)
  the Central Geological Survey, Ministry of
  Economic Affairs, (2) the Satellite Survey
  Division and Land Survey Bureau, Ministry of
  Interior, and (3) the Institute of Earth
  Sciences, Academia Sinica.
• The GPS measurements were collected within 232
  months before and 3 months after the mainshock of
  the Chichi earthquake.

Near-field co-seismic slant range displacement
estimated from GPS measurements. Error bar (95
confidence) in slant range has been added on each
station (data after Yu et al. 2001). Note that
the color code used is the same as that in the
figure before.
31

• Block diagram showing the tectonic setting of the
  Taichung area. The unwrapped interferogram is
  overlaid. The epicenter of the mainshock is shown
  as a red star.
• Slant range displacement along Profile AA
  derived from different approaches. The blue line
  represents the measurements from the InSAR
  method the red line represents the GPS
  measurements and the green line shows the
  displacement synthesized using the elastic
  dislocation model.
• The deformation gradient of Profile AA
  evaluated from the InSAR observations.
• The coherence of the images used along Profile
  AA.