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Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for Central US

Location

2003/12/29  09:02:08 38.13N 90.18W 5.0 3.0 ILLINOIS USGS

Location using ELOCATE and CUS model with fixed depth of 10 km

 STA  COMP DIS(K) AZM  AIN    ARR TIME             RES(SEC) WT QFM PHASE    WGT
 FVM    Z   27.34 227. 110. 20031229090214.322        -0.18  0 Eo P        0.72
 FVM    Z   27.34 227. 110. 20031229090218.110         0.06  0 Eo S        0.89
 JCMO   Z   40.60 287.  72. 20031229090215.820        -0.75  0 Eo P        0.32
 SLM    Z   54.02 356.  72. 20031229090225.411         0.15  0 Eo S        0.70
 SLM    Z   54.02 356.  72. 20031229090218.597        -0.07  0 Eo P        0.80
 CCM    Z   92.35 264.  72. 20031229090236.258         0.64  0 Eo S        0.20
 CCM    Z   92.35 264.  72. 20031229090224.862         0.20  0 Eo P        0.37
 SIUC   Z   98.71 119.  72. 20031229090224.718        -0.94  0 Eo P        0.14
 PVMO   Z  198.02 167.  48. 20031229090240.604         0.18  0 Eo P        0.18
 USIN   Z  222.73  95.  48. 20031229090310.573         2.36  0 Eo S        0.02
 USIN   Z  222.73  95.  48. 20031229090243.891         0.43  0 Eo P        0.11
 UTMT   Z  233.11 149.  48. 20031229090312.553         2.13  0 Eo S        0.02
 PLAL   Z  399.88 151.  48. 20031229090305.649         0.45  0 Eo P        0.06


 Error Ellipse  X=   1.1297 km  Y= 1.6529 km  Theta =   9.7920 deg

 RMS Error        :               0.221              sec
 Travel_Time_Table:          CUS
 Latitude         :             38.1510 +-    0.0103 N         1.1482 km
 Longitude        :            -90.1969 +-    0.0189 E         1.6401 km
 Depth            :               10.00 +-      2.71 km
 Epoch Time       :      1072688529.659 +-      0.21 sec
 Event Time       :  20031229090209.659 +-      0.21 sec

Focal Mechanism

The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
Figure 1. Location of broadband stations used to obtain focal mechanism


Focal Mechanism


  NODAL PLANES 

  
  STK=     129.99
  DIP=      69.99
 RAKE=      34.99
  
             OR
  
  STK=      26.53
  DIP=      57.39
 RAKE=     156.04
 
DEPTH 11.0 km
Mw = 3.00

Body-wave analysis

Body wave analysis was performed using codes from Computer Programs in Seismology, specifically the wvfgrd96 waveform mtch program

Data preparation

Digital data were collected, instrument response removed and traces converted to Z, R an T components.
Best mechanism fit as a function of depth. The preferred depth is given above. The sharp jump in fit is related to a lyeer boundary in the model at a depth of 10.0 km and the fact that the synthetics are fit at high frequencies, which means that the goodness of fit depends on matching distinct arrivals.

Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. The 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.

First motion data

The P-wave first motion data for focal mechanism studies are as follow:

Sta Az(deg) IO    Dist(km)   P-first motion
FVM  227   110      27        e- 
SLM  356    72      54        I+ 
CCM  264    72      92        I-
USIN  95    48     222        e+
SIUC 119    72      98        e+

Waveform comparison for this mechanism

The fits to the waveforms with the given mechanism are show below:

This figure shows the fit to the three components of motion (Z - vertical, R-radial and T - transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:

hp c 0.10 3
lp c 0.40 3

Discussion

The Future

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.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data.

Appendix A

The figures below show the observed spectral amplitudes (units of cm-sec) at each station and the theoretical predictions as a function of period for the mechanism given above. The CUS earth model was used to define the Green's functions. For each station, the Love and Rayleigh wave spectrail amplitudes are plotted with the same scaling so that one can get a sense fo the effects of the effects of the focal mechanism and depth on the excitation of each.

Last Changed Mon Dec 29 12:14:41 CST 2003