Location
2005/08/22 12:02:08 41.44N 12.50E 30 4.7 Italy
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
Focal Mechanism
SLU Moment Tensor Solution
2005/08/22 12:02:08 41.44N 12.50E 30 4.7 Italy
Best Fitting Double Couple
Mo = 1.10e+23 dyne-cm
Mw = 4.66
Z = 9 km
Plane Strike Dip Rake
NP1 250 85 10
NP2 159 80 175
Principal Axes:
Axis Value Plunge Azimuth
T 1.10e+23 11 115
N 0.00e+00 79 276
P -1.10e+23 3 24
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.21e+22
Mxy -8.13e+22
Mxz -1.44e+22
Myy 6.88e+22
Myz 1.53e+22
Mzz 3.31e+21
--------------
####-------------- P -
#######-------------- ----
########----------------------
###########-----------------------
############------------------------
##############------------------------
###############----------------------###
################--------------##########
#################--------#################
##################--######################
###############----#######################
##########---------#######################
#####--------------#####################
##------------------############### ##
--------------------############## T #
--------------------#############
--------------------##############
-------------------###########
-------------------#########
-----------------#####
--------------
Harvard Convention
Moment Tensor:
R T F
3.31e+21 -1.44e+22 -1.53e+22
-1.44e+22 -7.21e+22 8.13e+22
-1.53e+22 8.13e+22 6.88e+22
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/NEW/20050822120208/index.html
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INGV Rapid Moment Tensor
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the
station distribution are given in Figure 1.
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Figure 1. Location of broadband stations used to obtain focal mechanism
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 250
DIP = 85
RAKE = 10
MW = 4.66
HS = 9
The solution given here is from waveform inversion of regional vaeforms from the INGV digital seismic stations.
Waveform Inversion
The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.
The observed and predicted traces are filtered using the following gsac commands:
hp c 0.02 3
lp c 0.05 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 245 70 -15 4.36 0.2351
WVFGRD96 1.0 245 75 -15 4.39 0.2555
WVFGRD96 2.0 245 75 -15 4.47 0.3167
WVFGRD96 3.0 245 80 -10 4.51 0.3528
WVFGRD96 4.0 245 85 -5 4.54 0.3778
WVFGRD96 5.0 245 85 5 4.57 0.3977
WVFGRD96 6.0 245 85 5 4.60 0.4171
WVFGRD96 7.0 250 80 10 4.62 0.4289
WVFGRD96 8.0 250 80 10 4.64 0.4363
WVFGRD96 9.0 250 85 10 4.66 0.4386
WVFGRD96 10.0 250 85 10 4.67 0.4367
WVFGRD96 11.0 70 80 0 4.68 0.4322
WVFGRD96 12.0 70 80 0 4.69 0.4306
WVFGRD96 13.0 70 75 0 4.70 0.4284
WVFGRD96 14.0 70 75 -5 4.71 0.4272
WVFGRD96 15.0 70 75 -5 4.72 0.4254
WVFGRD96 16.0 70 75 -5 4.73 0.4189
WVFGRD96 17.0 70 80 -5 4.73 0.4161
WVFGRD96 18.0 70 80 -5 4.74 0.4135
WVFGRD96 19.0 70 80 -5 4.75 0.4110
WVFGRD96 20.0 70 80 -5 4.76 0.4052
WVFGRD96 21.0 70 75 -5 4.77 0.4039
WVFGRD96 22.0 70 75 -5 4.78 0.4000
WVFGRD96 23.0 70 75 -5 4.78 0.3957
WVFGRD96 24.0 70 80 -5 4.79 0.3923
WVFGRD96 25.0 70 80 -5 4.79 0.3888
WVFGRD96 26.0 70 80 -5 4.80 0.3818
WVFGRD96 27.0 70 80 -5 4.80 0.3784
WVFGRD96 28.0 85 80 -30 4.79 0.3748
WVFGRD96 29.0 85 80 -30 4.79 0.3722
WVFGRD96 30.0 80 80 -30 4.81 0.3696
The best solution is
WVFGRD96 9.0 250 85 10 4.66 0.4386
The mechanism correspond to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted.
Each observed-predicted componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed and because the velocity model used in the predictions may not be perfect.
A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow.
The bandpass filter used in the processing and for the display was
hp c 0.02 3
lp c 0.05 3
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Figure 3. Waveform comparison for depth of 8 km
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms.
Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure.
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First motion data
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion
ROM9 2 44 iP_C
CERT 35 70 eP_-
TOLF 329 81 iP_C
FIAM 29 106 iP_D
AQU 36 127 iP_D
INTR 61 133 eP_-
RNI2 77 141 eP_-
VAGA 90 145 eP_+
MIDA 80 148 eP_+
CII 77 154 eP_-
TERO 34 161 eP_-
SACS 343 165 eP_-
BSSO 85 175 eP_+
ARCI 332 179 eP_+
SACR 91 184 iP_C
FRES 71 190 iP_D
PSB1 96 195 iP_C
MURB 1 203 eP_X
MOCO 91 222 eP_X
CING 15 223 eP_-
CAFE 100 234 eP_-
SNAL 103 234 eP_X
MCRV 107 236 eP_X
MRLC 106 262 eP_-
VULT 101 267 eP_X
CUC 119 323 eP_+
FNVD 340 324 eP_X
BDI 333 331 eP_+
AMUR 98 349 eP_-
VLC 331 349 eP_+
NOCI 99 390 eP_+
TIP 123 440 eP_X
BOB 327 446 eP_+
Quality control
The follwoing stations were not used because of excessive low frequency noise in the deconvolved waveforms:
AMUR,
GIUL,
RNI2,
SNAL,
TRIV
Last Changed 2005/08/22