How to do

Summary

Continuous Waveforms

Downloading Data
Waveform Data Formats

SAC
miniSEED

Correction of the Instrumental Response

Dataless Format
Instrumental Correction

Downloading Data

(read the extended version)

Go into the Continuous Waveforms page;
select the Network Type [Permanent|Temporary];
select the Network Code;
press the Search button: the map and the station list at the bottom will update accordingly;
optionally, restrict your selection by using the other fields;
once ready, press the Select and Download Data button;
a new page will show the list of the selected stations;
select the desired stations and the time interval (use UTC time);
press the Check for Time Availability button;
a graphical representation of the available data will show up in a new page; if not satisfied, define a new time window and check again;
eventually, download the data either in miniseed or sac format by pressing one of the Extract buttons;
the extraction of the waveform data from the db can take some minutes: wait till it ends up;
once done, a system window will ask you to save the data: this action will download the data from the OASIS server into your computer. Make your choice and wait until this operation is terminated.

Top

The recorded signals are distributed in SAC or miniSEED formats. The channel code follows the SEED seismological standards ( Appendix A) and it identifies, respectively:
- first letter: the sampling (e.g.: S=62.5sps, E=125sps, H=100sps);
- second letter: the recording type (e.g.: H=velocity N=acceleration);
- third letter: the component (e.g.: E=EW, N=NS, Z=UP).
Top

SAC

The SAC (Seismic Analysis Code) files are named using the following convention:
YYYYJJJHHMMSS.SS.STAT.CHA, where the fields have the following meanings:

YYYY	Year
JJJ	Julian Day
HH	Hour
MM	Minute
SS.SS	Seconds.Fractional-Seconds
STAT	Station (three or four characters)
CHA	Channel

The time (YYYYJJJHHMMSS.SS) is referred to the time when the recording starts. For example the file 2007335070000.00.ACOM.HHZ refers to station ACOM, channel HHZ and the record begins on December 12, 2007 at 07:00:00.

The SAC software (see the SAC User's Guide) has functions for reading and processing these waveforms.
Top

miniSEED

The miniSEED (Standard for the Exchange of Earthquake Data) file names are named using the following convention:
STAT.CHA.YYYY.JJJ.HH.MM.SS, where the fields have the following meanings:

STAT	Station (three or four characters)
CHA	Channel
YYYY	Year
JJJ	Julian Day
HH	Hour
MM	Minute
SS	Seconds
STAT	Station (three or four characters)

The time YYYY.JJJ.HH.MM.SS refers to the time when the recording starts. For example the file ACOM.HHZ.2007.335.07.00.00 refers to station ACOM, channel HHZ and the record starts December 12, 2007 at 07:00:00.

The miniSEED files can be read, decompressed and converted in other formats (SAC, AH, CSS, ...) using the IRIS software rdseed. After installation, the software runs on your terminal and you must use d option and choose the output format; you can also select other preferences, the default is typed in brackets:

>rdseed
>Input Device (/dev/rst0): inputfile
>Output Device (stdout): tape.extraction.list
>Volume # [(1)-N]:
>Options [acsSrRtde]: d
>Station List (ALL):
>Channel List (ALL):
>Output format [(1-SAC),2-AH...]:
>Start Time(s) (FIRST):
>End Time(s) (LAST):
>Sample Buffer Length [2000000]:
>Extract Responses [Y/(N)]:

Rdseed reads miniseed file named 'inputfile' and convert it to other formats (SAC, AH, ...) with the options for selecting channel, station, start time and end time.
Top

CORRECTION OF THE INSTRUMENTAL RESPONSE

Dataless Format

In folder 'dataless' you can find the instrumental corrections in dataless format. More details can be found at the IRIS web site These files can be converted in other formats (RESP, Poles and Zeros, ...) using rdseed with the apposite options:

>rdseed
>Input Device (/dev/rst0): dataless
>Output Device (stdout): tape.extraction.list
>Volume # [(1)-N]:
>Options [acsSrRtde]: s
>Station List (ALL):
>Channel List (ALL):
>Network List (ALL) :
>Loc Ids (ALL ["--" for spaces]) :
>Output poles & zeroes ? [Y/(N)] :
>Extract Responses [Y/(N)]:

The response files ('.RESP') contains the whole history of the station with the corrections related to all instruments that recorded in the selected site from the starting date of the station to nowadays; the response files are divided for channel. The file names are named using the following convention:

RESP.NT.STAT..CHA

where the fields have the following meanings:

NT	Network
STAT	Station (three or four characters)
CHA	Channel

The PZ (Poles and Zeros) files are divided for channel and different instrument generates different PZ files. The file names are named using the following convention:

SAC_PZs_NT_STAT_CHA__YYYY.JJJ.HH.MM.SS.SSSS__ YYYY.JJJ.HH.MM.SS.SSSS

where the fields have the following meanings:

NT	Network
STAT	Station (three or four characters)
CHA	Channel
YYYY	Year
JJJ	Julian Day
HH	Hour
MM	Minute
SS.SSSS	Seconds.Fractional-Seconds

The first time refers to starting time for instrument, the second time refers to end time for the same instrument; if the instrument is operative end time is 99999.999.99.99.99.99999.
Top

Instrumental Correction

In this paragraph we describe the procedure to remove the instrumental response using SAC software and SAC formats; it is worth to evidence that the correction with the PZ files gives the results in displacement so you must differentiate the seismograms if you want velocity or acceleration. The procedure is:

>sac	... open the SAC software
SAC>read filesac	... read the recording file
SAC>rmean	... remove the mean
SAC>rtrend	... remove the trend
SAC>transfer from polezero S pzfile	... remove the instrumental response
SAC>dif differentiates	... if you want velocity
SAC>dif differentiates	... if you want acceleration
SAC>bandpass butter corner fmin fmax npoles n passes p	... filter the signal
SAC>write newfilesac	... save new corrected file
SAC>quit	... quit the SAC software

Top