The seismic data from the remote sites are transmitted via satellite to the SGS main station in Jeddah. The satellite channel is operated through commands from the SGS seismic center. Approximately 9 hours can be stored for three data channels by the transceiver system for retransmission requests in case of loss of some seismic data packets. The Ku band and VSAT satellite communication system used in the national network have proven to be very strong and can operate well even in severe dust storms and at high temperatures. Due to low precipitation, the loss of seismic data is rare. The main obstacles in the data retrieval system of the station are high temperatures, winds, and dusts, as high temperatures may cause the poor operation of the electronic devices, strong winds cause the antenna to move, and dusts cover the solar panels, reducing the efficiencies of their performance and causing frequent failures in the station.
The block diagram shows the flow of seismic data to the seismic data reception center of the SGS. The national network’s seismic data transmission and reception system a two-way transmittal system, designed to allow reverse commands to be sent from the main center to the seismic station, which allows the recovery of the seismic data, when these are lost after being checked and verified through the satellite communication system. It is possible to monitor the national network’s performance and efficiency in monitoring the seismic activities continuously and efficiently, thus, significantly contributing to the detection of malfunctions, so that necessary action can be done in the Saudi Geological Survey in Jeddah to ensure the continuous recording of seismic activities.
The flow of seismic data at the SGS NCEV.
Copies of all the data recorded in the stations are stored in their original form before any processing is carried out, so that they can be consulted or used for any application and research or studies. The storage process is done automatically on a daily basis on a large storage medium, and then, a monthly backup is created on external magnetic tapes. After the data are analyzed, they are stored in the database for all recorded earthquakes, for reference when needed. The National Center provides the data of the seismic waves recorded at the national network stations to some research and interested bodies in real time through secure contact points.
The Center’s staff can easily access the levels of the efficiencies of the stations by monitoring the performances and status of the batteries, seismic data loss, station breakdowns, and temperatures through a graphical user interface.
The Seismic Data Collection Division at the SGS NCEV.
The Seismic Data Analysis Division at the SGS NCEV.
The Atlas software is used for the processing and analysis of data on local earthquakes and the Hydra for the teleseismic earthquakes, both of which are classified as modern processing programs from the Nanometrics for the determination of amplitudes, time, and magnitudes.
Computer-analyzed earthquakes are plotted on maps and published in the SGS website, along with a list of already recorded and analyzed earthquakes, their coordinates, depths, time and date of their occurrences. Various models on crustal seismic velocities are used for the different regions of the Kingdom in order to obtain highly precise seismic parameters with low errors (kms) in determining the coordinates of the earthquakes outside the national network. The software can read SEED files, the internationally recognized standard format for the exchange of seismic data, can archive wave files of seismic events in an Oracle database, and can store them in a seismic data collection system, the APOLLOSERVER. It also allows the viewing of seismic waveforms on-screen and their processing very quickly and efficiently. The arrival times of the seismic waves can be picked up annually in each seismic monitoring station and filtered to enhance the seismic signal-to-noise ratio. Also, the epicenter and the magnitude of an earthquake can be easily plotted on the map using Atlas.
When earthquakes occur in the neighboring counties of Saudi Arabia, the data from the SGS seismograph network are added to the seismic data of other networks. The models for the velocity of seismic P waves in the crust and the upper mantle are then used in determining the seismic parameters, using the Hypoinverse software in Atlas, in order to delineate the location, source depth, time, and magnitude of an earthquake.
The seismograph stations should be well distributed around the earthquake in order to reduce the errors in locating its epicenter, especially that the crustal velocity model of seismic P waves represents only a general average, and thus, does not allow for details in regard to the different earth layers through which they travel. In general, most seismic events in western Saudi Arabia had been located accurately within a few kilometers from the current seismograph networks.