2010/07/16 09:04:47 39.167 -77.252 5 5.00 Maryland
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2010/07/16 09:04:47:4 39.17 -77.25 5.0 5.0 Maryland
Stations used:
LD.LUPA PE.PAGS PE.PSUB US.CBN
Filtering commands used:
hp c 0.05 n 3
lp c 0.2 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.53e+21 dyne-cm
Mw = 3.39
Z = 18 km
Plane Strike Dip Rake
NP1 195 57 123
NP2 325 45 50
Principal Axes:
Axis Value Plunge Azimuth
T 1.53e+21 62 159
N 0.00e+00 27 356
P -1.53e+21 7 262
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.68e+20
Mxy -3.13e+20
Mxz -5.70e+20
Myy -1.44e+21
Myz 3.99e+20
Mzz 1.17e+21
###########---
############----------
------------#---------------
-------------###--------------
-------------########-------------
-------------###########------------
-------------##############-----------
-------------################-----------
-------------#################----------
-------------###################----------
-------------####################---------
---------######################--------
P ---------######################--------
---------########## ##########------
-----------########## T ##########------
----------########## ##########-----
---------#######################----
--------#######################---
-------#####################--
------#####################-
----##################
-#############
Global CMT Convention Moment Tensor:
R T P
1.17e+21 -5.70e+20 -3.99e+20
-5.70e+20 2.68e+20 3.13e+20
-3.99e+20 3.13e+20 -1.44e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100716090447/index.html
|
STK = 325
DIP = 45
RAKE = 50
MW = 3.39
HS = 18.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2010/07/16 09:04:47:4 39.17 -77.25 5.0 5.0 Maryland
Stations used:
LD.LUPA PE.PAGS PE.PSUB US.CBN
Filtering commands used:
hp c 0.05 n 3
lp c 0.2 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.53e+21 dyne-cm
Mw = 3.39
Z = 18 km
Plane Strike Dip Rake
NP1 195 57 123
NP2 325 45 50
Principal Axes:
Axis Value Plunge Azimuth
T 1.53e+21 62 159
N 0.00e+00 27 356
P -1.53e+21 7 262
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.68e+20
Mxy -3.13e+20
Mxz -5.70e+20
Myy -1.44e+21
Myz 3.99e+20
Mzz 1.17e+21
###########---
############----------
------------#---------------
-------------###--------------
-------------########-------------
-------------###########------------
-------------##############-----------
-------------################-----------
-------------#################----------
-------------###################----------
-------------####################---------
---------######################--------
P ---------######################--------
---------########## ##########------
-----------########## T ##########------
----------########## ##########-----
---------#######################----
--------#######################---
-------#####################--
------#####################-
----##################
-#############
Global CMT Convention Moment Tensor:
R T P
1.17e+21 -5.70e+20 -3.99e+20
-5.70e+20 2.68e+20 3.13e+20
-3.99e+20 3.13e+20 -1.44e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100716090447/index.html
|
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.
|
|
|
|
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 0.05 n 3 lp c 0.2 n 3 br c 0.12 0.25 n 4 p 2The 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 60 40 2.89 0.2467
WVFGRD96 1.0 265 70 55 2.99 0.2625
WVFGRD96 2.0 260 60 50 3.07 0.2750
WVFGRD96 3.0 60 80 -5 3.11 0.2584
WVFGRD96 4.0 245 65 -25 3.04 0.2473
WVFGRD96 5.0 245 65 -30 3.07 0.2573
WVFGRD96 6.0 245 65 -35 3.11 0.2680
WVFGRD96 7.0 120 80 -35 3.12 0.2861
WVFGRD96 8.0 120 80 -40 3.15 0.3084
WVFGRD96 9.0 115 75 -40 3.18 0.3193
WVFGRD96 10.0 320 60 60 3.24 0.3199
WVFGRD96 11.0 315 60 60 3.25 0.3323
WVFGRD96 12.0 310 60 55 3.26 0.3416
WVFGRD96 13.0 315 55 55 3.29 0.3466
WVFGRD96 14.0 320 50 50 3.32 0.3483
WVFGRD96 15.0 315 50 50 3.32 0.3546
WVFGRD96 16.0 320 45 50 3.35 0.3585
WVFGRD96 17.0 325 45 50 3.38 0.3630
WVFGRD96 18.0 325 45 50 3.39 0.3667
WVFGRD96 19.0 325 45 50 3.40 0.3622
WVFGRD96 20.0 330 45 50 3.44 0.3478
WVFGRD96 21.0 330 45 50 3.45 0.3361
WVFGRD96 22.0 330 40 45 3.48 0.3287
WVFGRD96 23.0 335 35 45 3.50 0.3168
WVFGRD96 24.0 335 40 45 3.50 0.3076
WVFGRD96 25.0 330 40 35 3.51 0.3016
WVFGRD96 26.0 310 70 -40 3.41 0.2957
WVFGRD96 27.0 330 35 30 3.53 0.2981
WVFGRD96 28.0 325 15 15 3.53 0.2990
WVFGRD96 29.0 305 10 -5 3.53 0.3028
The best solution is
WVFGRD96 18.0 325 45 50 3.39 0.3667
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
hp c 0.05 n 3 lp c 0.2 n 3 br c 0.12 0.25 n 4 p 2
|
|
|
|
| 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values ISOTROPIC KGS FLAT EARTH 1-D CONSTANT VELOCITY LINE08 LINE09 LINE10 LINE11 H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Mon Apr 4 17:54:51 CDT 2011