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Seismic Data Processing


At the Mayagüez Seismic Network, digital data and analog registers (seismograms) are processed. When an event needs to be localized, one of the first steps is to identify if it is local, regional (MIDAS) or teleseismic. All earthquakes localized within latitudes 17ºN-20º N and longitudes 63.5ºW-69º W are considered local. The program used to localize events is called PR-HYPO. Event magnitudes are calculated using the maximum amplitude and registered duration times (CODA) that each station registers , using the Batailley von Hillebrandt (1993) formula, and using the velocity model proposed by Huérfano y Bataille (1994).

A. Local Events

All seismic events localized within latitudes 17-20º N and longitudes 63.5-69º W are considered local events. To determine the event location, P and S wave arrival times, wave polarity and lecture qualities are required. To determine the magnitude it is necessary to read the duration (CODA) and the maximum amplitude of the waveforms registered by each station that detected the event.

PRSN Location example using PR-HYPO format
Year mo da origin lat n lon w depth rms erh erz gap Xma Fma MM
2000-02-22 1200 20.67 18 44.82 66 52.39 62.6 .08 1.14 1.07 266 4.5 4.9 IV

sta cha dist azm an p/s w sec+ccor (tobs -tcal -dly =res) wt xmg fmg info
APR shz 35.6 154 148 EP+ 1 31.38 .00 10.71 9.99 .00 .72 .00 3.6 2.7 .000
S 2 38.22 .00 17.55 17.48 .00 .06 .85 .000
AGP shz 47.2 217 140 EP- 1 31.57 .00 10.90 10.85 .00 .05 1.27 .000
S 2 39.58 .00 18.91 18.99 .00 -.08 .85 .000
LRS shz 50.5 176 138 EP? 1 31.66 .00 10.99 11.13 .00 -.14 1.27 3.6 3.0 .000
S 2 40.20 .00 19.53 19.48 .00 .05 .85 .000
LSP shz 67.2 200 129 EP+ 1 33.46 .00 12.79 12.65 .00 .14 1.27 .000
S 2 42.79 .00 22.12 22.14 .00 -.02 .85 .000
CELP shz 80.9 157 123 EP+ 1 34.66 .00 13.99 14.05 .00 -.06 1.27 .000
S 2 45.22 .00 24.55 24.59 .00 -.04 .85 .000
PORP shz 81.0 162 123 EP+ 1 34.66 .00 13.99 14.06 .00 -.07 1.27 3.2 2.6 .000
S 2 45.34 .00 24.67 24.60 .00 .06 .85 .000
CSB shz 91.2 123 120 EP+ 1 35.82 .00 15.15 15.15 .00 .00 1.27 .000
S 2 46.77 .00 26.10 26.51 .00 -.42 .13 .000
CPD shz 128.1 127 111 EP? 1 40.08 .00 19.41 19.35 .00 .06 1.27 3.5 3.1 .000
S 2 54.61 .00 33.94 33.86 .00 .07 .85 .000

At the PRSN database, time series are maintained in PC-SUDS format (for seismic events recorded using IASPEI), SOUFRIERE-native, WGSN and GSE-1, the last two formats are used for events recorded using the ViSeis system. All catalogue event solutions of the PRSN have been transformed into PR-HYPO format.

For all seismic events that have not been digitally recorded, P y S waves, CODA and amplitude data is read directly from seismograms and used in a subroutine of the PRLOC application that allows event location using manual data entry. After the data is pre-localized, lecture residual errors, rms, vertical (erz) and horizontal (erh) are checked. If necessary, the seismogram is read again and the event is relocalized. The process is repeated until the best possible location result is obtained. Once these steps are completed, event processing is done, and its location is registered in our seismic events database, which can be accessed thru this webpage. Our data is used to complete seismic events databases of other networks (i.e. MIDAS Consortium) in our service lists. The data is then used on research projects by local and international institutions.

B. Regional Events

Seismic events whose epicenters are localized out of the local zone (lat. 17-20º N and long. 63.5-69º W) and within latitudes 5º S -35º N and longitudes 55-125º W are considered regionalevents (MIDAS region).

There are three different processing steps for regional events:

1- If the seismic event was reported using the USGS automatic location system, arrival times are determined, and the data is submitted as quickly as possible to the MIDAS system to determine the final location.

2- Once the final location is determined by USGS or PRSN, the phases recorded on the digital system are determined and maintained on the General Catalogue.

Location example of a regional event
Year Mo Da Hr Mi Sec Lat Lon Depth Mb Ms Source
1999-12-01-19-23-13.26 18.11 -82.47 33.0 5.8 PDE
Region: Caribbean Sea
Sta Delta Phase Polarity Weight Min Sec Res
CELP 15.11 Pn + 2 26 37.8 -6.4
MGP  14.62 Pn + 2 26 32.0 -5.7
PORP 15.05 Pn - 2 26 36.9 -6.5
SJG  15.51 Pn - 2 26 49.5 -0.3
CSB  15.49 Pn - 2 26 43.0 -6.2
LSP  14.61 Pn - 2 26 33.2 -4.4

3-If phases are registered but there is no location, arrival times are analyzed and distributed to all regional networks as part of the MIDAS cooperation project.

C. Teleseismic Events



PRSN Teleseismic Events example

SOURCE:             NEIC
DATE (yyyy/mm/dd):  2004/08/07
TIME (hh:mm:ss.ss): 09:30:16.45
LATITUDE:           51.814
LONGITUDE:          -66.464
DEPTH:              10.0
REGION:             South of the Aleutian Island
Mw:                 6.0
Mb:                 6.3
Ms:                 5.4
Ml:                 0.0
QUAKE STATIONS:     180
RSPR PHASES: 13
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