The information below describes the St Louis 
University original earthquake catalog.

***************************************

THE ST. LOUIS UNIVERSITY MICROEARTHQUAKE NETWORK 
EVENT FILE

Each epicenter has a two 'card' entry. The first 
line gives event location and the second gives a 
general comment. 

740629    92709.5 36.36 89.28  5.0* 2.0  3  4 285  17 0.40  0.       embayment  
hornbeak,tn                                                       
740704   135806.3 36.25 89.51  5.0* 1.5  4  6 143   8 0.52 10.       embayment  
caruthersvill,mo                                                  
740707   171317.7 36.80 89.01  5.0* 2.3  3  6 289  70 0.39 52.3      embayment  
wickliffe,mo-ky                                                   
740707   210208.4 36.75 89.06  5.0* 1.9  3  6 285  63 0.50 74.9      embayment  
wickliffe,mo-ky                                                   
740709    41536.1 36.54 89.69  5.0* 1.3  3  4 190  39 0.59  0.       embayment  
new madrid,mo                                                     
880311 1 2143 5.7337.15489.106 8.9  2.8 13 25 121  49  0.4  0.9  1.5 cc    UPL D
OLMSTED, IL       mbLg(3Hz)=2.6<FVMZ>                                                                   
880315 1 123448.7638.30389.00311.8  2.8 11 22 145  83  0.3  0.9  1.2 bd    EMB D
WOODLAWN, IL      mbLg(3Hz)=2.5<FVMZ>                                                                   
880319 1 223223.7536.21689.456 7.4  2.8 23 36  93   6  0.2  0.5  0.7 bb    EMB D
MISTON, TN        mbLg(3Hz)=2.8<FVMZ>                                                             
880329 1  33036.9036.01389.867 6.5  2.1 15 30  72   8  0.3  0.7  1.1 cb    EMB D
STEELE, MO        mbLg(3Hz)=2.1<FVMZ>                                                             
880329 1 232410.7236.14089.736 1.0  2.3 14 24  83  20  0.4  0.7  0.9 cc    EMB D
CARUTHERSVILLE, MOmbLg(3Hz)=2.1<FVMZ>                                                             


The entries per column and FORTRAN FORMAT are

FIRST LINE:

COLUMN	FORMAT	Description
1:6	i6	DATE (YRMNDY)
8       a1      FELT FLAG
10:11	i2	HOUR
12:13	i2	MINUTE
14:18	f5.2	SECOND
19-24	f6.3	LATITUDE
25-30	f6.3	LONGITUDE (NOTE NUMBERS INDICATE WEST)
31-34	f4.1	DEPTH (KM)
35-35	a1	* IF FIXED DEPTH
36-39	f4.1	MAGNITUDE
40-42	i3	NUMBER STATIONS
43-45	i3	NUMBER PHASES
46-49	i4	ANGULAR GAP
50-53	i4	MINIMUM DISTANCE (km)
54-58	f5.1	RMS (sec)
60-63	f4.1	ERH (km)
65-68	f4.1	ERZ (km)
70-70	a1	QUALITY Hypo 71 quality factors
71-71	a2	QUALITY
76-78	a3	FLAG INDICATING EARTH MODEL USED
80-80	a1	FLAG (D=digitally recorded event; 
                C=teleseism cross correlation) 
                (prior to 1980 - the last 8 columns
                had the earth model e.g., EMBAYMENT)

SECOND LINE:
    a80     comment about quadrangle, intensity, 
            magnitude

Here is an extract of a program to read the data, 
latitude and longitude

        data fmt(1:28)/'(i6,1x,a1,1x,2i2,f5.2,f6.3,'/
        data fmt(29:59)/'f6.3,f4.1,a1,f4.1,2i3,2i4,f5.1,'/
        data fmt(60:88)/'1x,f4.1,1x,f4.1,1x,2a1,4x,a3,'/
        data fmt(89:100)/'1x,a)       '/
        read(5,fmt)iymd,ifelt,ihr,imin,sec,xlat,xlon,depth,
     1	ifix,xmag
     2	,nr,np,igap,idmin,rms,erh,erz,quals,quald,flag,cortel
        eplat = xlat
        eplon = -xlon
 9002   format(a)
        read(2,9002,end=9999,err=9999)icmnt

The hypocenters from the SLU network are determined
using a modified version of FASTHYPO (Herrmann, 
1979). This program uses first P arrivals principally
in conjunction with Geiger's method to determine 
hypocenter locations by minimizing the residuals 
between observed and calculated P arrival times. 
Usually S wave arrivals are also used in the 
computation of the hypocenter as an additional 
constraint on the solution. The most accurate 
solutions are for those events that occur within 
the physical dimensions of the network. For events
outside the network the accuracy depends upon 
distance from the network and the relation of
the source of the event to the network geometry.

Concerning the identification and location of events, all
signals recorded by the network have been carefully screened
in order to eliminate those from man-made sources. Most
numerous of the latter are signals from strip mine explosions
and quarry blasts. These are recorded at the rate of ten
to thirty per day, so the discrimination between explosions
and earthquakes is importatnt. A large ratio of S wave
to P wave amplitude, lower frequency content, and a
well developed dispersive train of surface waves are found
to be characteristic of explosion signals. The sequence
of arrivals across the network and the time of data of
occurrences are also helpful in distinguishing explosions
from earthquakes (see Has, Lotte, Michael Ellis and
Paul A. Rydelek, 1992).

The SLU estimated epicenters for teleseisms have been 
determined by a location procedure outlined by Herrmann
(1982). The procedure chooses an arbitrary reference
coordinate within the array and by assuming a plane wave
across the network, determines the back azimuth and
dt/d(DEL). Then, by using travel time curves which
assume a focal depth of 15 km, the value of Delta (DEL)
is determined. Using spherical trigonometry, epicentral
coordinates are then determined given back azimuth
and delta. However, the use of a fixed focal depth
definitely contrains the accuracy of the locations.
In the future amplitude and period information will be
used.

Information on the Catalog:

A "D" preceding the origin time indicates that the event
was recorded by the PDP 11/34 and that digital trace data
are available.

ORIGIN TIME; All origin times are given in Coordinated 
Universal Time (UTC). For Central Standard Time and Central
Daylight Savings Time subtract 6 and 5 hours respectively.

LAT and LON - Epicentral coordinates in degrees.

DEPTH - Focal depth of earthquake in km. AN * following 
the focal depth implies that the focal depth is restricted
to that value in the computation of the hypocenter.
When good station coverage is lacking, five kilometers
has been found to be an appropriate value for events
in the center of the embayment, whereas a 10 km focal depth
is generally used outside this area.

MAG - An average of the displacement magnitudes computed
for each station. The formulae used to compute magnitudes
were developed under attenuation studeis funded by NSF.
Three sets of magnitude relations are used. The amplitude of
ground motion used in each case is for sustained maximum
of S wave train. Ground motion is expressed in millimicrons
for the first formulae and in microns for the last. Beginning
in 1983 more detailed instrument response curves at higher
frequences are used with digital data. A comparative
study indicates that previously published 10 Hz magnitudes
may have been underestimated by 0.2 magnitude units. The
notation has been altered as suggested by Herrmann and Kijko (1983).
The formulae are as follow:

1. For magnitudes determined by records from the network
(Microearthquake responses) telemetered stations, the formulae
used apply to signals in the period range 0.08 sec <=T<=0.12 sec
and for Embayment events only.

	MLG (10HZ) = 0.95log(DEL)+log(A) -1.05
                    DEL in km
                    A in millimicrons
                    10km<=DEL<=40km
	MLG (10HZ) = 1.25log(DEL)+log(A) -1.50
                    DEL in km
                    A in millimicrons
                    40km<=DEL<=100km
	MLG (10HZ) = 1.55log(DEL)+log(A) -2.10
                    DEL in km
                    A in millimicrons
                    100km<=DEL<=200km
	MLG (10HZ) = 2.50log(DEL)+log(A) -4.30
                    DEL in km
                    A in millimicrons
                    200km<=DEL<=300km

2. For magnitudes determined by records from near regional 
stations (S.P. WWSSN response, e.g. FVM, CGM) and for
periods 0.2 sec<=T<=0.50 sec

	MLG (3HZ) = 0.88log(DEL)+log(A) -1.00
                    DEL in km
                    A in microns
                    10km<=DEL<=100km
	MLG (3HZ) = 1.06log(DEL)+log(A) -1.36
                    DEL in km
                    A in microns
                    100km<=DEL<=200km
	MLG (3HZ) = 1.29log(DEL)+log(A) -1.89
                    DEL in km
                    A in microns
                    200km<=DEL<=400km

3. For all other stations, and for period 1 +/- 0.4 seconds:

	MBLG = 3.75 + 0.90 log (DEL) + log(A)
                    DEL in degrees
                    A in microns
                    0.5 degrees<=DEL<= 4 degrees 
	MBLG = 3.30 + 1.66 log (DEL) + log(A)
                    DEL in degrees
                    A in microns
                    4.0 degrees<=DEL<= 30 degrees 
For further information on magnitudes in central United States
see Nuttli (1973).

4. Relations 1-2 are equivalent to correcting for Q and Lg
propagation to distance of 10 km

                  a10 = A(DEL/10)**(5/6)e**(gamma*DEL)
where
               gamma = pif/Q(3.55)
where
    Q = 1500(f/1.0Hz)**0.2. Magnitude is defined by:
             MLG(f) - log10a10 + 5.00 -5.06.

Nuttli(personal communication) defines an MB = 5.0 earthquake as
one having 115 microns of motion at a distance of 10 kilometers
from the epicenter. Relation 4 has been demonstrated to work
in the Central United States (Herrmann and Nuttli, 1982).

Stations used: These indicate the number of stations and
number of phases, respectively that were used in the computation
of the epicenter.

AZIMUTHAL GAP - The largest azimuthal aperture in degrees
for stations recording the event.

MINIMUM STATION DISTANCE - Epicentral distance in km to 
neartest eatsion

QUAL - Quality factory fro HYPO71 (Lee et al, 1972).

Crustal Model - Because of the varied geologies of the 
Mississippi Embayment and the Ozark Uplands, two velocity
models are used to compute hypocenters. These are based
on drill logs and observation data available in 1974.
While more recent investigations by the USGS have 
given better models, these old models are used for 
consistency in the catalog. All hypocenters are first 
computed with the EMBAYMENT mode. Any events withch fall 
outside the geological boundaries of the Mississippi
Embayment are then recomputed with the UPLANDS
model to refine their location. For events that must
be located graphically, Nuttli's model is used to refine
their location. 5 km focal depth is assumed.

The Crustal model used for each solution is given as
EMB (Embayment), UPL (Uplands), NUT (Nuttli) 

  Model              Depth             P-velocity
                      km                km/sec

NUTTLI             0-20                  6.15
                   20-40                 6.70
                   40-97                 8.18
                   halfspace             8.37

EMBAYMENT          0-1                   2.80
                   1-1.5                 3.60
                   1.5-2.0               5.60
                   2.0 - 20              6.15
                   20 - 40               6.70
                   40 - 97               8.18
                   halfspace             8.37

UPLANDS            0 -2                  5.60
                   2 - 20                6.15
                   20 - 40               6.70
                   40 - 97               8.18
                   halfspace             8.37

RMS ERROR TIME: Root mean square error of the time
residuals in seconds:

          RMS = SQRT(SUM(Ri*Ri/N)
where Ri is the observed arrival time minus the computer
arrival time at the ith station.

STD ERROR DIST
  Standard error of the epicenter in kilometers

           STD = SQRT(SDX*SDX + SDY*SDY)
where SDX and SDY are the standard errors in latitude and
longitude, repsectively. It should be kept in mind that STD
gives an indication of the accuracy of the relative locations
of the hypocenters. Systematic errors due to uncertainties
in the velocity models will cause the relative locations and
absolute locations to be inconsistent.

STD ERROR DEPTH - Standard error of the focal depth in km.

Distance arrival quality and residual weight are used
for the solution and in specifying RMS, STD ERROR DIST
and STD ERROR DEPTH.

                 REFERENCES

Dwyer J.J. R.B. Herrmann, C. Nicholson and O.W. Nuttli, (1979)
Time domain scaling and magnitude relations in the Central
United States, Eos, 60, 875.

Hass, Lotte, Michale Ellis, and Paul A. Rydelek, (1992)
Minimum Magnitude of completeness and rates of seismicity
in the New Madrid region. Seismological Res. Let., 63,(3), 
395 - 405.

Herrmann, R.B.(1979). FASTHYPO - A Hypocenter location 
program Earthquake Notes, 50, 25 - 38.

Herrmann, R.B., (1982). Digital processing of regional data,
BSSA, 72, S261 - S276.

Herrmann, R.B. and A Kijko (1983) Short period Lg magnitudes:
instrument attenuation and source effects, BSSA 73. 1835 - 1850.

Lee, H.K. and J.C. Lahr (1972). HYPO71 - A computer program
for determining hypocenters USGS Open-File Report, 100 p

Leu, (1985) Magnitude corrections for the Central Mississippi
Valleyu Seismic Network. M.S. Thesis Saint Louis University.

Nuttli, O.W. (1973) Seismic wave attenuation and magnitude
relations for eastern North America, J. Geophys. Res.
78, 876 - 885.

Nuttli, O.W., W.Stauder, C. Kisslinger (1969). Travel time
tables for earthquakes in the Central United States, Earth-
quake notes, 40, 19-28.