THE DEVELOPMENT OF THE ROMANIAN VLF/LF MONITORING SYSTEM AS PART OF THE INTERNATIONAL NETWORK FOR FRONTIER RESEARCH ON EARTHQUAKE PRECURSORS (INFREP)

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1 EARTH PHYSICS THE DEVELOPMENT OF THE ROMANIAN VLF/LF MONITORING SYSTEM AS PART OF THE INTERNATIONAL NETWORK FOR FRONTIER RESEARCH ON EARTHQUAKE PRECURSORS (INFREP) I.A. MOLDOVAN 1, A.P. CONSTANTIN 1, P.F. BIAGI 2, D. TOMA DANILA 1, A.S. MOLDOVAN 3, P. DOLEA 4, V.E. TOADER 1, T. MAGGIPINTO 2 1 National Institute for Earth Physics, P.O.Box MG-2, RO , Magurele, Romania, irenutza_67@yahoo.com, angela@infp.ro 2 Department of Physics, University of Bari, Italy 3 AZEL Designing Group, Magurele, Romania 4 BITNET Research Center on Sensors and Systems, Cluj Napoca, Romania Received January 30, 2015 The Romanian VLF / LF monitoring system consists in a radio receiver and the infrastructure that is necessary to record and transmit the collected data, and is part of the international initiative INFREP and was put into operation in December 2009 on the Black-Sea shore (Dobruja Seismologic Observatory Dob-RO). Since then the system was developed by replacing the vertical antenna with a magnetic loop-type one, by installing a vertical electric field monitor and a weather station, and by designing special software for the transfer, storage and initial processing of data using the LabView software platform. Key words: Seismogenic zones, earthquakes, electromagnetic waves, radio propagation paths. 1. INTRODUCTION Research on the possible correlation between seismic activity and ionospheric disturbances have been intensified in the last decade, having as turning point the seismo-ionospheric coupling models presented by [1] in Different coupling models have been developed both before and after 2004 [2 8], all of them pointing the existence of ionospheric anomalies prior to earthquakes. Interests in these studies were caused by the increasing quality of observation data by using advanced equipment and a consistent ionospheric monitoring activity, both at ground and space level [9 12] and also advanced processing techniques for phenomena correlation [12 14]. Processes that occur during the preparation phase of a forthcoming earthquake determine a particular lithosphere-ionosphere coupling and produce variation of the medium in which radio signals propagate, affecting especially electromagnetic propagation in the lower ionosphere, in the VLF (3 30 khz) and LF (30-300kHz) bands ([12] and [14]). Rom. Journ. Phys., Vol. 60, Nos. 7 8, P , Bucharest, 2015

2 1204 I.A. Moldovan et al. 2 In the current scientific context, the International Network for Frontier Research on Earthquake Precursors INFREP [12] has developed its activities into two directions: (i) implementing of an interconnected European network of radio VLF/LF receivers for a comprehensive collection of useful information on lower ionosphere properties, (ii) data processing and identification techniques for preseismic signatures on electromagnetic anomalies. The network of VLF/LF receivers constitutes an innovative approach, meant to reveal the connection between the ionosphere s disturbances and the preparatory stage of earthquakes whose activation zone intersects the 5th Fresnel zone of the propagation path between VLF/LF transmitters and the receivers [15, 16]. At the moment the network consists in eleven receivers located all over Europe (Portugal, Italy, Malta, Greece, Romania, Turkey and Cyprus Fig. 1 and Table 1). Table 1 Characteristics of the INFREP receivers and the frequencies monitored in 2014 Ri Sign Location Lat R1 CIP Nicosia, Cyprus R2 CRE Chania, Crete, Greece R3 MAL Valletta, Malta R4 POR Evora, Portugal R5 R6 TUR GRE Canakkale, Turkey Thesaloniki, Greece R7 IT-Tc Santeramo, Italy R8 IT-Du Duronia, Italy R9 IT-An Antrodoco, Italy R1 0 R1 1 IT-Mi Dob- RO Miano, Italy Eforie Nord, Romania Lo ng Start date 3/2012 4/ / /2010 4/ / /2012 LFi T1,T2,T4,T9, T8 T1,T2,T4,T9, T8 T1,T2,T4,T9,T 8 T1,T2,T9,T8,T 7 T1,T2,T4,T9, T11 T1,T2,T4,T9, T7 T1,T2,T4,T9,T 8, T11 VLFi T10, T13,T14,T6, T5 T13, T14,T6,T5, T12 T10,T13,T14,T12 T10,T13,T14,T5 T10,T13,T12, T6,T5 T13,T14,T12, T6,T5 T10,T13,T14,T6, T5??? 11/ /2012 9/2009 T1,T4,T9,T8,T 11, T3 T2,T11,T9, T8 T4 T11, T8,T7, T4 T10,T13,T14,T6, T5 T10,AWT09,AWT 04, T14,T6,T5 T10,T13,T14,T12 T5, AWT25 The equipment is produced by the Italian company Elettronika S.R.L. [17]. Each receiver monitors 10 frequencies distributed in the VLF (15~50 khz) and LF (150~300 khz) bands emitted by high power transmitters located throughout Europe (Fig. 1 and Table 2).

3 3 The development of the Romanian VLF/LF monitoring system 1205 During the INFREP functioning period only 10 earthquakes with Mw > 6.0 occurred, the largest being the Mw = 6.9 event, occurred on 24 th of May 2014, in the Agean Sea (event number 10 from Fig. 1). For each frequency, the receiver saves the power level detected on a non-volatile memory at a customizable sample time interval. The large amount of data collected by the VLF/LF radio receiver is organized in text files, one for each day. Fig. 1 The receivers (Ri) of INFREP, the LF and VLF monitored transmitters (Ti), and the European earthquakes with Mw > 6.0 occurred after 2009 (Table 5). The data (sampling rate of 1min) are downloaded automatically at the end of each day and they are stored and processed in the server located at the Department of Physics of the University of Bari (Italy) that is the central node of the network. The present paper will detail the 5 years development of the Romanian VLF/LF monitoring system as part of the International Network for Frontier Research on Earthquake Precursors (INFREP). The final structure of the Romanian electromagnetic monitoring system should become a model of a complex and complete functional radio receiving site that might be adopted by all the INFREP partners.

4 1206 I.A. Moldovan et al THE ROMANIAN VLF/LF MONITORING SYSTEM AS PART OF INFREP 2.1. INSFRASTRUCTURE DEVELOPMENT MAGNETIC FIELD ANTENNAS INSTEAD OF ELECTRIC ONES During the summer of 2009 the Romanian radio receiver location was fixed in one of the most Eastern parts of Romania, on the Black-Sea shore, at the Dobruja Seismologic Observatory (Dob-RO) (Fig. 1). The first development of the equipment was imposed by the high level of the local electromagnetic noise generated either by the high-voltage aerial lines surrounding the observatory or by the specific electric properties of the local atmosphere, which is rich in salt aerosols. Table 2 The transmitters monitored by INFREP/AWESOME receivers Ti Sign Location Lat Long Freq (Hz) Type T1 TRT Polatli, Turkey LF T2 RRO Brasov, Romania LF T3 RRU Taldom, Russia LF T4 CZE Topolna, Czech LF T5 ITS Niscemi, Italy VLF T6 ICV Tavolara, Sardinia VLF T7 CH1 Ouargia, Algeria LF T8 T9 T10 MCO EU1 DHO Roumoules, France Felsberg-Berus, Germany Rhauderfehn, Germany LF LF VLF T11 FRI Allouis, France LF T12 HWU Le Blanc, France VLF T13 GBZ Anthorn, UK VLF T14 NRK Keflavik, Iceland VLF AWT04 GBZ Anthorn, UK VLF AWT9 HWV StAssise, France VLF AWT25 TBB Bafa, Turkey VLF After some local tests we put into evidence that the noisy behavior of the receiver was due to the electric-field antennas, which weren t suitable for that site. In July 2009 we have decided to make the replacement of the electric-type

5 5 The development of the Romanian VLF/LF monitoring system 1207 antennas with magnetic-type ones (Fig. 2) [18]. The antennas designing and verification process has taken a couple of months. During this time the whole receiving chain was also verified using a programmable signal generator and others specific lab-testing devices. Fig. 2 The new loop magnetic antennas with preamplifiers into operation in Dobruja Observatory (Dob-RO). After all the modifications were done and after 2 months of tests, at the end of 2009, the VLF / LF antennas and the receiver were installed in the final site and it started to record good data, even in the highly electric-polluted environment at the Dobruja Observatory (Fig. 2) INSFRASTRUCTURE DEVELOPMENT INSTALLATION OF A VERTICAL ELECTRIC FIELD MONITOR During the summer of 2010, we have installed a new system to monitor the fluctuations of the vertical atmospheric electric field in the same site with the VLF/LF system, to have a clear evidence of the periods with high local electromagnetic noise. The hardware is a Boltek EFM100, atmospheric electric field monitor. In Fig. 2, the monitor is situated on the top of loop antennas. Adding the electrometer was a necessity since the monitored area is very unstable from electric and electro-atmospheric point of view. Once the electrometer was installed it was proven that there exists large diurnal variations of the atmospheric electric field. Measuring the static electric field the Boltek EFM-100 not only detects diurnal variations but also detects

6 1208 I.A. Moldovan et al. 6 sudden changes of the electric field due to nearby lightning and thunderstorms. In Fig. 3 are presented the local electric field variations at Dob-Ro in comparison with another low noise monitoring site, situated in the Vrancea mountains, far away from electric perturbations DOB-RO-BOLTEK August PLOR4-BOLTEK August 2010 E (KV/m) E (KV/m) E (KV/m) DOB-RO-BOLTEK September 2010 E (KV/m) PLOR4-BOLTEK September 2010 Fig. 3 Electric field measurements emphasizing the local electric field noise from Dob-Ro. As one can see for DOB-Ro there are long period variations of 10 days and amplitudes changes from 20 kv/m to +10 kv/m. Moreover, the high frequency noise is also very large about 4 5 KV/m from 40 KV/m (the recording scale) means 20 db. On the opposite side, the data recorded at PLOR4 are very clean. The electric field doesn t have diurnal, nor long or short period variations. In PLOR4 site only the weather and the tectonic conditions are influencing the time evolution of the electric field intensity. The noise is of only 0.1 kv/m, from the total electrometer scale of 40 kv/m, giving a noise level less than 50dB. Observing the atmospheric electric field recordings we have had the confirmation of a previous theory, which was assuming that the bad quality of the VLF/LF data was due to local conditions, regarding the activity of this local electric field. Changing the electric-type antennas with magnetic-type ones (loop antennas) was an appropriate solution toward a proper receiving of the VLF/LF electromagnetic waves in Dob-RO site that presents atmospheric electric field anomalies INSFRASTRUCTURE DEVELOPMENT INSTALLATION OF A WEATHER STATION Nearby the VLF/LF antennas and the electric field monitor we have also installed in January 2011 a WS-3600 weather station for monitoring the meteorological influences like temperature, pressure and humidity (Fig. 4).

7 7 The development of the Romanian VLF/LF monitoring system 1209 Fig. 4 WS-3600 weather station and atmospheric parameters variations during the first month of monitoring. At this moment, the INFREP radio receiver, the Boltek electric field monitor and the weather station are working well without errors and all the data are processed together for a better correlation between the electromagnetic recordings and the local conditions DATA RECORDING/TRANSMISSION/ARCHIVING At present, the Elettronika receiver installed at Dob-RO is connected to Internet at a fixed IP address and is accessible from anywhere in the world. To avoid the data loss, the receiver is supplied from an uninterruptible power supply which ensures autonomy of approximately 3 hours and provides a good immunity to the power surges it may appear. The recorded data are consistent and reliable. All the data are recorded on local scale: the electromagnetic VLF/LF data on the storage device of the receiver and the electric and weather data on the hard disks of local computers. All the data are transmitted in real time by internet to the data center of NIEP-Magurele for storage and advanced analysis at the headquarters from Magurele. The radio VLF/LF data are downloaded daily from the receiver from Eforie and processed in correlation with European seismicity DATA MONITORING EVOLUTION Since it was put into operation, on 1 st of December 2009, the radio data were monitored and archived without any interruptions, until the end of November 2010 when an error occurred leading to a data gap of two months.

8 1210 I.A. Moldovan et al. 8 Table 3 The monitored frequencies by the Dob-RO radio receiver during time Period (starting with) Monitored frequencies (Hz) 22/12/ /07/ /11/2010 N N N N N N N N N N 01/02/ /03/ /10/ /10/ /05/ /06/2014 N N N N N N N N N N 21/07/ Ti GBZ T13 GBZ / /ICV/ /TBB T13 //T6/ /AWT25 HWU DHO NRK ITS (NSI) FRI/ CH1 EU/FRI MCO CZE T12 T10 T14 T5 T11/T7 T9/T11 T8 T4 Another interruption of one month and a half of data archiving was in the summer of 2014, when the local thunder storms, have damaged the transmission equipments, so we could not access for a while the receiver for data downloading and cleaning of the memory storage (Table 3). 3. CORRELATION OF THE ROMANIAN MONITORED RADIO PATHS WITH THE EUROPEAN SEISMICITY The most destructive seismic events in Europe occur in the Mediterranean countries, particularly Greece, Italy and Turkey. Albania, Romania and Bulgaria (especially the Shabla source in the Black Sea region) have also experienced major earthquakes. From those seismic sources, the Romanian receiver is passing over parts of Romania, Bulgaria, North Greece, South and North Italy, but most of the paths monitored by the Romanian receiver are not crossing seismogenic area, being used as reference recordings, that are not influenced by tectonic activity. The VLF / LF receiver installed at Dobrudja Observatory (Dob-RO) has monitored different frequencies during time as can be seen in Tables 3 and 4.

9 9 The development of the Romanian VLF/LF monitoring system 1211 Dob-RO Period (starting with) Table 4 The monitored frequencies by the Dob-RO radio receiver during time Monitored frequencies (Hz) T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T13 T14 A25 22/12/2009 x x - x x x x x x x x - 19/07/2010 x x - x x x x - x x x x - 30/11/ /02/2011 x x - x x x x - x x x x - 01/03/2011 x x - x x - x x x x x x - 03/10/2011 x x - x x - x x x x x x - 04/10/2011 x x x x x - x x x x - x - 01/05/2012 x x - x x - x x x x - x x 01/06/ /07/2014 x x - x x - x x x x - x x The configuration of sampled frequencies by the Romanian receiver is presented in Fig. 5 in correlation with the European seismicity with Mw > 6 occurred in the last 100 years. Fig. 5 The seismogenic zones crossed by the 5 th Fresnel zone of the radio paths monitored by the DOB-Ro receiver.

10 1212 I.A. Moldovan et al. 10 Table 5 Earthquakes with Mw > 5.5 occurred in Europe in the INFREP functioning period Date Time UTC Lat Long Depth Mw Region Name No 09/02/16 23:16: IONIAN SEA 09/04/06 1:32: CENTRAL ITALY 1 09/04/07 17:47: CENTRAL ITALY 09/06/19 14:04: EAST MEDITERRANEAN SEA 09/07/01 9:30: CRETE 2 09/09/06 21:49: ALBANIA 09/11/03 5:25: IONIAN SEA 09/12/17 1:37: WEST OF GIBRALTAR 10/04/11 22:08: SPAIN 3 11/04/01 13:29: CRETE 4 11/05/19 20:15: WESTERN TURKEY 11/09/22 3:22: EASTERN TURKEY 11/11/23 12:17: CRETE 12/04/16 11:23: SOUTHERN GREECE 12/05/11 18:48: CYPRUS REGION 12/05/20 2:03: NORTHERN ITALY 5 12/05/22 0:00: BULGARIA 12/05/29 7:00: NORTHERN ITALY 12/05/29 10:55: NORTHERN ITALY 12/06/10 12:44: DODECANESE ISLANDS 12/07/09 13:54: EAST MEDITERRANEAN SEA 13/01/08 14:16: AEGEAN SEA 13/06/15 16:10: CRETE 6 13/06/16 21:39: CRETE 13/10/12 13:11: CRETE 7 13/12/28 15:21: CYPRUS REGION 14/01/26 13:55: GREECE 8 14/02/03 3:08: GREECE 9 14/04/04 20:08: SOUTHERN GREECE 14/05/24 9:25: AEGEAN SEA 10 14/08/01 4:11: NORTHERN ALGERIA

11 11 The development of the Romanian VLF/LF monitoring system 1213 In Table 5 are presented only the earthquakes occurred in Europe in the INFREP functioning period. From 31 seismic events with Mw > 5.5, only 10 have moment magnitudes larger than 6.0. From those 10 events only 3 events could be studied in correlation with the radio propagation paths monitored by the Romanian receiver. From Fig. 5, one can see that only the preparation zones [15] of earthquakes 5, 8 and 9 (Table 6) can be barely associated with the 5 th Fresnel zone [21] of the radio paths between the transmitters and the Romanian receiver. Table 6 Earthquakes that might be associated with the radio paths monitored by Dob-Ro Ev. No. Date Mw Frequencies 5 12/05/ T8/MCO/ T11/FRI/ T12/HWU/ /01/ T5/ITS/45900 T7/CH1/ /02/03 6 T5/ITS/45900 T7/CH1/ DATA PROCESSING In Figs. 6, 7 and 8 are presented some results of our studies, for the period preceding the earthquakes from Table 7. Table 7 North Italy and Bulgaria earthquakes with Mw > 4.0, from May 2012 and from late October 2012 Date Day of the year Hour Lat Long Dept (km) Mw Source May /05/ :03: N Italy 12/05/ :18: N Italy 12/05/ :02: N Italy 12/05/ :37: N Italy 12/05/ :00: BULGARIA 12/05/ :30: BULGARIA 12/05/ :04: BULGARIA October /10/ :35: EAST MED SEA 12/10/ :20: GREECE 12/10/ :05: SOUTHERN ITALY 12/10/ :16: GREECE

12 1214 I.A. Moldovan et al. 12 All the catalogues were obtained from the EMSC web page. All the magnitudes were converted into moment magnitude Mw, using equations 1 [19] and 2 [20]. 2 Mw = Ms = M L 0.018M L (1) Mw = Ms = 1.59 mb 3.97 (2) Fig. 6 Recordings at Dob-RO, of the LF characteristics and European seismicity (Mw > 4.5) during May Fig. 7 Recordings at Dob-RO of the vertical electric field during May The events from Table 7, occurred on May 20 th with Mw = 6.1 in Italy (event 5 from Tables 5 and 6) and May 22 nd, 2012 with Mw = 5.6 in Bulgaria, near Sofia, inside the sensitive area monitored by the Romanian receiver. As seen

13 13 The development of the Romanian VLF/LF monitoring system 1215 from Fig. 5, and Table 6, the anomalies should be visible on MCO, FRI and HWU (traces marked with blue on Figs. 6 and 8) for the earthquakes occurred in the Northern part of Italy and on ITS and CH1 for the Bulgarian earthquakes. On LF (Fig. 6), there are visible anomalies during 18 and 19 of May, on almost all traces but MCO, where the signal is very disturbed during the whole month. MCO transmitter has always a strange behavior with higher amplitudes during the day than during the night, but usually, the signal is not so noisy like it was in May The geomagnetic indices are not so high during 18 and 19 of May as they were during May 9 th (the daily Kp = 36), but one can see on the electric recordings (Fig. 7) a very large disturbance, specific for very stormy days, exactly during the anomaly recorded on CH1, FRI and CZE. So the anomaly can not be related to the LF propagation characteristics perturbed by the precursory stage of an earthquake or by the magnetic storms, but to the local electric conditions. Fig. 8 Recordings at Dob-RO of the VLF characteristics, and the European seismicity (Mw > 4.5) during May 2012.

14 1216 I.A. Moldovan et al. 14 On the VLF recordings (Fig. 8), on HWU frequency there is no visible anomaly on these type of representation, prior to the series of earthquakes from 20 and 22 May 2012, from Italy. In the ITS signal, one can see nighttime disturbances on May 9, 16 and 30, but the anomalies should not be interpreted as seismoionospheric signals, because this is a behavior often observed on 45900Hz recordings, and might be correlated with some peculiarities of the Italian transmitter, that are recorded also by other INFREP receivers, like the one from Greece, Thessaloniky. 4. CONCLUSIONS In the case of the Romanian receiver installed at Dob-RO, due to the highly electric-field polluted environment and to the specific, local, conditions the original VLF / LF receiver installed at Dobruja Observatory produced unsatisfactory output data. By modifying its input stage topology (antennas and preamplifiers) we have obtained an improvement of its response, resulting in better data quality. The new installed magnetic-field antennas are less susceptible to parasitic electric fields that are produced by the high-voltage aerial lines surrounding the installation site. They are also less susceptible to the electrical proprieties of the local propagation medium, than the electric-field antennas were. At a primary data examination and in the case of a single parameter monitoring site, the increases or decreases of radio intensities could be falsely interpreted as seismic precursors, but the complex simultaneous monitoring of different fields (local vertical electric and atmospheric) can easily reject the false alarms. The complex monitoring of the local conditions at the receiving site should become a condition of functioning of the INFREP system. The future development of the Romanian part of INFREP network aims to solve new aspects and open problems related to isolation of seismic zones and identification of their specific characteristic that influence the ionospheric perturbations for European sources, but especially for the Romanian ones. For example, installing a receiver in the Bucovina region, would isolate the effects of Vrancea area and would create the possibility for differential analysis of propagation data spread over several directions, toward the existing transmitters in Western Europe. Relatively large distance between the two receivers would provide an opportunity to examine seismic zones not only inside our country, but also outside it, because the perspective offered by the two sets of propagation paths is substantially different. To make a fine description, two receivers would provide a "stereoscopic view" of ionospheric activity anomalies recorded above European seismic zones. Another useful future development of the Romanian system is to adopt the processing approaches of INFREP partner and to analyze the VLF/LF radio data (diurnal variations, sudden changes, long period perturbations, etc) using more advanced techniques for correlation with the associated phenomena.

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