2005/04/23 19:11:41 39.46N 16.83E 19 4.1 Italy
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2005/04/23 19:11:41 39.46N 16.83E 19 4.1 Italy
Best Fitting Double Couple
Mo = 4.62e+22 dyne-cm
Mw = 4.41
Z = 30 km
Plane Strike Dip Rake
NP1 270 80 -45
NP2 10 46 -166
Principal Axes:
Axis Value Plunge Azimuth
T 4.62e+22 22 327
N 0.00e+00 44 80
P -4.62e+22 38 219
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.12e+22
Mxy -3.22e+22
Mxz 3.07e+22
Myy 2.35e+15
Myz 5.68e+21
Mzz -1.12e+22
############--
##################----
#### ###############------
##### T ################------
####### #################-------
############################--------
##############################--------
###############################---------
###############################---------
################################----------
###-----------------------------#######---
--------------------------------##########
--------------------------------##########
------------------------------##########
------------------------------##########
--------- ----------------##########
-------- P ---------------##########
------- --------------##########
---------------------#########
------------------##########
-------------#########
------########
Harvard Convention
Moment Tensor:
R T F
-1.12e+22 3.07e+22 -5.68e+21
3.07e+22 1.12e+22 3.22e+22
-5.68e+21 3.22e+22 2.35e+15
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/NEW/20050423191141/index.html
|
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
|
|
|
|
STK = 270
DIP = 80
RAKE = -45
MW = 4.41
HS = 30
The solution given here is from waveform inversion of regional vaeforms from the INGV digital seismic stations.
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 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 85 35 -75 3.94 0.3440
WVFGRD96 1.0 80 40 -85 3.97 0.3630
WVFGRD96 2.0 80 40 -80 4.05 0.4309
WVFGRD96 3.0 95 40 -60 4.09 0.4374
WVFGRD96 4.0 105 40 -45 4.11 0.4371
WVFGRD96 5.0 130 75 5 4.08 0.4388
WVFGRD96 6.0 105 90 55 4.15 0.4609
WVFGRD96 7.0 110 85 50 4.15 0.4977
WVFGRD96 8.0 115 80 55 4.20 0.5299
WVFGRD96 9.0 120 75 55 4.21 0.5625
WVFGRD96 10.0 115 75 50 4.22 0.5916
WVFGRD96 11.0 120 70 50 4.23 0.6196
WVFGRD96 12.0 130 60 55 4.26 0.6410
WVFGRD96 13.0 120 65 50 4.25 0.6602
WVFGRD96 14.0 125 60 50 4.26 0.6756
WVFGRD96 15.0 120 60 45 4.27 0.6872
WVFGRD96 16.0 120 60 45 4.27 0.6982
WVFGRD96 17.0 115 65 45 4.26 0.7049
WVFGRD96 18.0 110 70 40 4.26 0.7110
WVFGRD96 19.0 105 75 40 4.26 0.7151
WVFGRD96 20.0 105 75 35 4.27 0.7183
WVFGRD96 21.0 110 70 40 4.31 0.7218
WVFGRD96 22.0 105 75 40 4.32 0.7254
WVFGRD96 23.0 105 75 40 4.32 0.7276
WVFGRD96 24.0 100 80 40 4.34 0.7307
WVFGRD96 25.0 95 85 40 4.36 0.7334
WVFGRD96 26.0 95 90 40 4.36 0.7366
WVFGRD96 27.0 95 90 40 4.37 0.7400
WVFGRD96 28.0 275 85 -40 4.38 0.7435
WVFGRD96 29.0 275 85 -40 4.39 0.7462
WVFGRD96 30.0 270 80 -45 4.41 0.7516
The best solution is
WVFGRD96 30.0 270 80 -45 4.41 0.7516
The mechanism correspond to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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
|
|
|
|
| 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. |
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion TIP 191 32 iP_C CEL 212 156 eP_X MRLC 322 184 eP_X CLLN 318 190 eP_+ SNAL 320 213 eP_X MRB1 320 243 eP_X PSB1 319 260 eP_X SACR 321 281 eP_X BSSO 321 299 eP_X VAGA 315 309 eP_X TRIV 324 321 eP_X MIDA 319 326 eP_X CII 320 330 eP_X TIR 50 332 eP_X FRES 328 334 eP_X RNI2 319 337 eP_X INTR 320 376 eP_X CERT 312 427 eP_X AQU 319 432 eP_X FIAM 316 442 eP_X TERO 323 444 eP_X WDD 208 448 eP_X
The follwoing stations were not used because of excessive low frequency noise in the deconvolved waveforms: AMUR, GIUL, RNI2, SNAL, TRIV