Operation of the Norwegian National Seismic Network 2008

Operation of the

Norwegian National Seismic Network

2008

Supported by

University of Bergen

and

Norwegian Oil Industry Association

Prepared by

Department of Earth Science University of Bergen Allegaten 41, N-5007 Bergen

March 2009

CONTENTS

1. Introduction 2

2. Operation 2

3. Field stations and technical service 3

4. NNSN plans 2009 6

Appendix 1 Seismicity of Norway and surrounding areas

Appendix 2 The NORSAR regional arrays

1. Introduction

This annual report describes the operation of the Norwegian National Seismic Network (NNSN) for the year 2008. It covers operational aspects as well as a financial report for all seismic stations operated by the Department of Earth Science at the University of Bergen (UiB), which has the responsibility of the NNSN.

The network is supported by the oil industry through the Norwegian Oil Industry Association (“Oljeindustriens Landsforening” (OLF)) and the University of Bergen (UiB).

The seismicity of Norway and surrounding areas is presented in Appendix 1. The seismic arrays operated by NORSAR are covered in Appendix 2 of this report. NORSAR is subcontracted to deliver data of interest to NNSN.

2. Operation

The operational stability for each station is shown in Table 1. The average downtime for all stations during this reporting period is 1.3 % compared to 2.1 % in 2008. This is acceptable since the goal of average downtime is below 2%.

Table 1. Downtime in % for 2008 for all stations of the NNSN.

Station Downtime in % Lofoten (LOF) 1,5 Askøy (ASK) 0 Mo i Rana (MOR8) 0 Bergen (BER) 0 Molde (MOL) 1 Bjørnøya (BJO) 1 Namsos (NSS) 0 Blåsjø (BLS) 0 Odda (OOD1) 4 Dombås (DOMB) 0 Oslo (OSL) 2,5 Rundemanen (RUND) 7,5 Espegrend (EGD) 0 Snartemo (SNART) 3 Florø (FOO) 10 Stavanger (STAV) 0 Flostrand (FLOS) 0 Steigen (STEI) 0 Homborsund (HOMB) 0 Stokkvågen (STOK) 0 Hopen (HOPEN) 2 Sulen (SUE) 4 Høyanger (HYA) 0 Blussvoll (TBLU) 0 Jan Mayen BB (JMI) 0 Tromsø (TRO) 0 Jan Mayen SP (JMI) 0 Average 1,3 Jan Mayen (JNE) 0 Jan Mayen (JNW) 0 Karmøy (KMY) 6 Kautokeino (KTK) 0

Station Downtime in % Kings Bay (KBS) 1 Kongsberg (KONO) 0,5 Konsvik (KONS) 0

2 3. Field stations and technical service

The technical changes for each seismic station are listed below. It is noted if these changes are not related to a visit from the technical staff at the University of Bergen. When a station stops working, tests are made to locate the problem. Sometimes the reason cannot be found and the cause of the problem will be marked as unknown.

Bjørnøya (BJO1) No visit or technical changes.

Blussvoll (TBLU) 13.11.08 Visit. A new station located in Trondheim, was installed with the following equipment: 1 PC optiplex 170L ST: GB1732J with Seislog for Linux. 1 Skjerm 19" LCD 1 Guralp SN:T6278 4GB CMG-6TD-001 15.12.08. New Sensor/digitizer T6281 512 Mb CMG-T6D-0003 replaced by local operator.

Blåsjø (BLS) 07.05.08. Visit. New digitizer (ED2400), GPS, Dell PC, Seislog for Linux, was installed. By a mistake damping resistance was not installed. 21.05.08. Damping resistance, 5.6 Kohm, was installed by the local operator.

Dombås (DOMB) 06.11.08. ADSL was installed and connected to a new PC (industr.), 1 SARA SADC 20 Digitizer and GPS. When starting, no input signal. After some testing it turned out that the signal cable was broken. Tried to fix the cable without succeeding. A new signal cable has to be installed next visit. 18.11.08. A new signal cable (black) was installed. This time a 3 comp SARA Digitizer, s/n MAT322, 2 Hz geofones was installed in the aluminium box. Inside the building, a new Guralp Digitizer CMG- DM24-S3, ser. no. A1219 was installed. PC is Seislog for Linux

Florø (FOO) 01.01 – 06.02.08. A malfunctioning digitizer caused low S/N level. Attempts were made to fix the problem remotely. Station down for 37 days. 07.02.08. Visit. A new ED2400 digitizer, a new Dell PC with Seislog for Windows was installed. A PC replaced the Lap Top. The 3 SS-1 Rangers sensors were replaced with a new BB sensor, Trillium 120P. The aluminium box was wet inside, cleaned it up.

3 Flostrand (FLOS) No visit or technical changes.

Homborsund (HOMB) 21.11.08. Visit. A new station, located 15 km southwest of Grimstad, was installed with the following equipment: 1 Industrial PC with Seislog for Linux 1 Nanometrics Trillium 120P S/N 0427 1 Guralp CMG-DM24-2000 S/N A1225 1 Power supplies Mascot 6823, 500mA.

Hopen (HOPEN) 6 – 14.01.08. Station down for 8 days due to a malfunction PC. 14.01.08. A new PC was installed by the local operator. 30.09.09. New Linux PC and connection to internet by Satellite Communication, installed by the local operator. Høyanger (HYA) No visit or technical changes.

Jan Mayen (JMI) No visit or technical changes.

Karmøy (KMY) 10.09.08. PC restarted at 11:55 by the local operator. No data lost.

Kautokeino (KTK) No visit or technical changes.

Kings Bay (KBS) No visit or technical changes.

Kongsberg (KONO) No visit or technical changes.

Konsvik (KONS) No visit or technical changes.

Lofoten (LOF) 18. – 21.01.08. Restarted PC by use of the Telecommander. Station down for 3 days. Reason unknown. 22. – 25.03.08. Station down for 3 days. Reason unknown. 23.07.08. New Dell PC, Seislog for Linux, was installed by the local operator. Data transferred by ADSL line.

Mo i Rana (MOR8) No visit or technical changes.

4 Molde (MOL) 07. 11.08. A new PC, Seislog for Linux was installed to replace the old PC Seislog for Windows.

Namsos (NSS) No visit or technical changes. Odda (ODD1) 07.05.08. Visit. A new Dell PC with Seislog for Linux was installed. 22.05.08. When the PC was set up, the sample rate had a mismatch to the digitizer. Changed the sample rate from 50 Hz to 100 Hz. Data lost 7-22/5-08. Station down for 15 days.

Oslo (OSL) 1 – 11.01.08. Station down for 10 days. Reason unknown.

Rundemanen (RUND) 15.01.08. Station down since 01.01.08 due to error on digital line. During February and March digital line unstable. 18.06.08. Visit. The line converted from digital to analog. Installed 1 PTS-3 box (Sprengnether). Gain 84 dB, filter 5-10Hz. 5V full scale.

Snartemo (SNART) 23.07.08. Noise 50 Hz. Replaced the Digitizer SADC 20, but still 50 Hz noise without finding the source. 09.10.08. Noise on Z and EW component. Corrosion on the vertical seismometer. Dismantled and cleaned the seismometer, cleaned also the NS and EW seismometer. Noise ok.

Stavanger (STAV) 11.-12.06.08. Visit. Installed new Dell PC with Seislog for Linux, new digitizer (Nanometrics RD3). The data are now transferred on a ADSL line. 17. – 30.06.08. A new digitizer (RD3) was replaced by the local operator. Station down for 14 days due to a malfunctioned digitizer.

Steigen (STEI) No visit or technical changes.

Stokkvågen (STOK) No visit or technical changes.

5 Sulen (SUE) 30/1 – 14.02.08. Station down for 15 days. Reason unknown.

Tromsø (TRO) No visit or technical changes.

WNN network: Bergen (BER), Espegrend (EGD), Ask (ASK), Rundemanen(RUND)

18.06.08. Rundemanen (RUND) replaced Bergen (BER) in the WNN network. 23.09.08. Visit. Windows-PC was replaced with Linux-PC. The reason is that Seislog for Linux has problems with the ED2400 digitizer.

4. NNSN-plans 2009

Plans and progress for 2008:

 Plan: Convert the whole network to a real time network, include 10 stations from Finland, Denmark and the UK, 4 stations from NORSAR and install 2 new stations to form an approximately 45 station real time network. The location of all seismic stations can be seen in Figure 1. o Progress: 42 stations are now in real time, the remaining will be included once the communication is available. Two new stations are installed, HOMB and TBLU.  Plan: Store all continuous data from all stations in the NNSN data base. o Progress: Completed for 42 stations, remaining will be included when communication is ok.  Plan: Include NORSAR array detections in real time system. o Progress: No new software has been made by NORSAR yet to enable this function since all emphasis was put in getting real time digital data.  Plan: Move all real time processing and data storage to new Linux system. o Progress: Completed  Plan: Upgrade network with 10 new digitizers. o Progress: 4 Digitizers have been installed.  Odda (ODD) is upgraded with ADSL connection and the data are now transferred in real time.  Høyanger (HYA) is upgraded with new equipment i.e. PC (industrial quality) running Linux Seislog and digitizer.  Blåsjø (BLS) is upgraded with new equipment.  Dombås (DOMB) is upgraded with ADSL.  Namsos (NSS) is upgraded with new equipment.

6 Currently the upgraded ISDN stations (BLS, HYA, KTK, NSS, and SUE) work in semi real time, meaning data is transmitted within 15 minutes. For this reason they do not participate in the triggersystem, but all data is stored.

The last station in NNSN without internetcommunication, Hopen, finally got a satellite link in the fall. This was done in cooperation with the University of Tromsø and the Meteorological Institute. Communication costs will be quite high compare to the other stations (56 kNOK/year).

The main problem in the transition to the new network has been the difficulty in obtaining ADSL lines to the stations. New lines must be ordered centrally at the UIB and this combined with the new company providing communication (Ventelo) has delayed the installation of communication. After a few months of frustration, we were allowed to use other companies and are now also using Telenor and NexeGenTel. Finally there are sites where ADSL is not available and we are currently testing two types of mobile phone connections.

The other problem making slowing down the progress has been the late delivery of the new digitizers. Unfortunately this is a type of equipment which cannot be easily obtained elsewhere. As replacement, lower quality digitizers have been used in some of the stations.

The moving of the data collection and processing system to a new platform is now complete although minor problems still remain. This task and setting up of the real time communication, has used most of the technical resources in 2008. Figure 2 shows a flow diagram of the NNSN real time data acquisition.

NNSN real-time data acquisition Linux LINUX SERVER station SEISLOG Seedlink SeedLink Server EarthWorm SEISAN continous Seedlink server 24-hour Continous Input data from data files SeedLink server Windows Re-transmission Triggering station Liss continous Communication Helicorder plots SEISLOG with other Seedlink servers.

SEISNET SEISAN DATABASE

Figure 2. Diagram showing the NNSN real time data flow.

Figure 1. Stations contributing to the NNSN database. Norwegian stations with yellow circles are BB stations. NNSN stations: red triangles, NORSAR stations: blue triangles, British, Danish and Finnish stations transmitting signals in real time: green triangles and station marked with white triangle is to be installed in 2009.

Plans for 2009

♦ UiB

 Sulen (SUE) will be upgraded with ADSL, line is ready but modem has not yet been installed. New equipment, including PC and digitizer, will be installed.  Install a new Broad band station in Finmark.  Karmøy KMY will get new equipment, mobile phone solution will be tested  Mo i Rana (MOR) will get new equipment, mobile phone solution will be tested.  Test mobile phone solution for the following stations: Høyanger (HYA), Blåsjø (BLS), Kautokeino (KTK), Karmøy (KMY), Mo i Rana (MOR)  Minor upgrade on several stations.

There are two more ADSL station (SUE ans NSS) to be installed. GSM mobile phone solutions, today used on 2 stations near Stokvågen (FLOS and KONS), are a bit too slow to provide reliable data since there is no 3G coverage at these sites. This is also the case for the remaining 5 sites and ICE (communication based on old NMT network) solutions will be tested. However it is now doubtful that ICE can be used due to economical problems at ICE.

♦ NORSAR

 Develop the prototype of an event detection system to be integrated with NNSN.  Improve joint processing.

♦ NORSAR-NNSN joint analysis work

The NORSAR analyst is, on a daily basis, merging the NORSAR local recordings into the NNSN database and relocates the event.

♦ Other  Develop joint web pages  Offshore stations. There is an ongoing effort to connect one sensor from Ekofisk and plans to install a new sensor at Statfjord

Progress Report No. 1-2008

for

Norwegian National Seismic Network

January 1st to June 30th, 2008.

Supported by

Norwegian Oil Industry Organization

and

University of Bergen, Department of Earth Science

Prepared by

Department of Earth Science University of Bergen Allegaten 41, N-5007 Bergen

October 2008

1. Introduction

This progress report, under the project Norwegian National Seismic Network (NNSN), covers the first half of 2008. The purpose is to describe the current technical operation of the stations and the data recorded for the first half of 2008.

2. Operation

The operational stability for each station is shown in Table 1. The average downtime for all stations during this reporting period is 2.1 % compared to 1.6 % in the same time period of 2007. This is acceptable since the goal of average downtime which is below 2%.

Table 1a. Downtime in % for the period 1/1-30/6 2008 for all stations of the NNSN.

Station Downtime in Steigen (STEI) 0 % Stokkvågen 0 Askøy (ASK) 0 (STOK) Bergen (BER) 0 Sulen (SUE) 8 Bjørnøya (BJO) 2 Tromsø (TRO) 0 Blåsjø (BLS) 0 Average 2,1 Dombås (DOMB) 0 Espegrend (EGD) 0 Florø (FOO) 20 Flostrand (FLOS) 0 Hopen (HOPEN) 4 Høyanger (HYA) 0 Jan Mayen BB (JMI) 0 Jan Mayen SP (JMI) 0 Jan Mayen (JNE) 0 Jan Mayen (JNW) 0 Karmøy (KMY) 0

Kautokeino (KTK) 0 Kings Bay (KBS) 2,1 Kongsberg 1,1 (KONO) Konsvik (KONS) 0 Lofoten (LOF) 3 Mo i Rana (MOR8) 0 Molde (MOL) 0 Namsos (NSS) 0 Odda (OOD1) 8 Oslo (OSL) 5 Rundemanen 15 (RUND) Snartemo (SNART) 0 Stavanger (STAV) 0

3. Field stations and technical service

Bjørnøya (BJO1) No visit or technical changes.

Blåsjø (BLS) 07.05.08. Visit. New digitizer (ED2400), GPS, Dell Pc, Seislog for Linux, was installed. By a mistake damping resistance was not installed. 21.05.08. Damping resistance, 5.6 Kohm, was installed by the local operator.

Dombås (DOMB) No visit or technical changes.

Florø (FOO) 01.01 – 06.02.08. A malfunctioning digitizer caused low S/N level. Attempts were made to fix the problem remotely. Station down for 37 days. 07.02.08. Visit. A new ED2400 digitizer, a new Dell PC with Seislog for Windows was installed. The PC replaced the Lap Top. The 3 SS-1 Rangers sensors were replaced with a new BB sensor, Trillium 120P. The aluminium box was wet inside, cleaned it up.

Flostrand (FLOS) No visit or technical changes.

Hopen (HOPEN) 6 – 14.01.08. Station down for 8 days due to a malfunction PC. 14.01.08. A new PC was installed by the local operator.

Høyanger (HYA) No visit or technical changes.

Jan Mayen (JMI) No visit or technical changes.

Karmøy (KMY) No visit or technical changes.

Kautokeino (KTK) No visit or technical changes.

Kings Bay (KBS) No visit or technical changes.

Kongsberg (KONO) No visit or technical changes.

Konsvik (KONS) No visit or technical changes.

Lofoten (LOF) 18. – 21.01.08. Restarted PC by use of the Telecommander. Station down for 3 days. Reason unknown.. 22. – 25.03.08. Station down for 3 days. Reason unknown. Mo i Rana (MOR8) No visit or technical changes.

Molde (MOL) No visit or technical changes.

Namsos (NSS) No visit or technical changes.

Odda (ODD1) 07.05.08. Visit. A new Dell PC with Seislog for Linux was installed. 22.05.08. When the PC was set up, the sample rate had a mismatch to the digitizer. Changed the sample rate from 50 Hz to 100 Hz. Data lost 7-22/5-08. Station down for 15 days.

Oslo (OSL) 1 – 11.01.08. Station down for 10 days. Reason unknown.

Snartemo (SNART) No visit or technical changes.

Steigen (STEI) No visit or technical changes.

Stokkvågen (STOK) No visit or technical changes.

Sulen (SUE) 30/1 – 14.02.08. Station down for 15 days. Reason unknown.

Tromsø (TRO) No visit or technical changes.

WNN network: Bergen (BER), Espegrend (EGD), Ask (ASK), Rundemanen(RUND)

18.06.08. Rundemanen (RUND) replaced Bergen (BER) in the WNN network.

4. Data

Figure 1 shows earthquakes and explosions recorded during the first half of 2008 and located within the shown area.

Figure 1. Epicentre distribution of located events recorded during January – June 2008. Earthquakes are plotted in red and presumed and known explosions in yellow.

st A major earthquake (MW=6.0) occurred February 21 , 2008 at 02:46 (UTC) south of Spitsbergen. This earthquake was the largest recorded in the history in Norway apart from the plate boundary events. The epicentre was located to 77.16N and 19.89E, at Storfjordsbanken. This earthquake was strongly felt in Longyearbyen were people woke up. This earthquake was followed by several aftershocks of which many were recorded at several stations and could be located. The largest of these aftershocks occurred April 11th with magnitude 4.3. Figure 2 shows 246 earthquakes located within the mapping area and occurring during the first 6 months of 2008. The closest seismic stations are the SVAESS array at Spitsbergen (~140 km) and Hopen (~150 km). The seismic station at Hopen recorded approx. two thousands aftershocks in the following months. These small earthquakes have not been processed.

Figure 2. Epicentre distribution (Jan.-Jun.) of located events recorded after the magnitude 6.0 earthquake in February 2008.

5. NNSN-plans 2008/2009

Plans and progress for 2008:

 Plan: Convert the whole network to a real time network, include 11 stations from NORSAR, Finland and the UK and install 2 new stations to form a 44 station real time network. (see Figure 3) o Progress: 34 stations are now in real time, the remaining will be included once the communication is available.  Plan: Store all continuous data from all stations in the NNSN data base. o Progress: Done for 34 stations, remaining will be included when communication is ok.  Plan: Include NORSAR array detections in real time system. o Progress: No new software has been made by NORSAR yet to enable this function since all emphasis has been in getting real time digital data. This task will be started in November, 2008.  Plan: Move all real time processing and data storage to new Linux system. o Progress: Done.  Plan: Upgrade network with 10 new digitizers. o Progress: Digitizers were ordered in spring, have not yet arrived.  Plan: Install one new broad band station in S. Norway and install a station at a Trondheim school. o Progress: The chosen site is located in Homborsund, Grimstad and the station will be installed in November. The Trondheim station will also be installed in November. It was not possible to install earlier due to communication problems at the school.

Figure 3. Stations contributing to the NNSN database. Stations marked with yellow triangles are to be installed in 2008.

The other problem making progress slow has been the late delivery of the new digitizers which were promised to arrive July 1. Now they are supposed to arrive at November 7th. Unfortunately this is a type of equipment which cannot be easily obtained elsewhere. As replacement, lower quality digitizers have been used in some places.

The moving of the data collection and processing system to a new platform is now complete although minor problems still remain. This task and setting up of the real time communication, has used most of the technical resources so far this year. Figure 4 shows a flow diagram of the NNSN real time data acquisition.

SEISNET SEISAN DATABASE

Figure 4. Diagram showing the NNSN real time data flow.

Plans for remaining stations for 2008 – early 2009

♦ UiB

 Odda (ODD) will be upgraded with ADSL, line is ready but modem has not yet been installed.  Karmøy KMY will get new equipment, mobile phone solution will be tested  Høyanger (HYA) will get new equipment, mobile phone solution will be tested  Sulen (SUE) will be upgraded with ADSL, line is ready but modem has not yet been installed.  Blåsjø (BLS) has got new equipment, mobile phone solution will be tested.  Bjørnøya will get new equipment, communication is ready but a new PC (Linux) must be installed.  Dombås (DOMB) will be upgraded with ADSL, line is ready. A 3 component sensor and new equipment will be installed.  Namsos (NSS) will get new equipment, mobile phone solution will be tested.  Mo i Rana (MOR) will get new equipment, mobile phone solution will be tested.  Kautokeino, mobile phone solution will be tested.

There are 3 more ADSL station to be installed and 5 stations will be equipped with a mobile phone solution. GSM mobile phone solutions, today used on 2 stations near Stokvågen (FLOS and KONS), are a bit too slow to provide reliable data since there is no 3G coverage at these sites. This is also the case for the remaining 5 sites and ICE (communication based on old NMT network) solutions are therefore tested. So far it looks good and the first test on a field station will be made in November. If all goes well, it might be possible to get most of the remaining stations online in real time this year.

♦ NORSAR

 Finalize system of delivery of data to NNSN with a SEEDlink server  Develop the prototype of an event detection system to be integrated with NNSN

♦ NORSAR-NNSN joint analysis work

Since the network only recently has become in full operation (all NORSAR data entered middle of October), little testing has been done with this processing. One person from NORSAR has spent nearly 2 weeks in Bergen leaning the joint processing system and the plan is that NORSAR will participate in the general processing for the rest of the year. Based on this experience, further plans will be made for next year.

♦ Other

Offshore stations. There is an ongoing effort to connect one sensor from Ekofisk and plans to install a new sensor at Statfjord

Seismicity of Norway and surrounding areas

for

2008

Prepared by

Department of Earth Science University of Bergen Allegt. 41 N-5007 Bergen

e-mail: [email protected] Phone: (+47) 55 58 36 00 Fax: (+47) 55 58 36 60

March 2009

CONTENTS

1. Introduction 3

2. Velocity models and magnitude relations 4

3. Events recorded by the Norwegian stations 7

4. The seismicity of Norway and adjacent areas 8

5. Felt earthquakes 20

6. Use of NNSN data during 2008 22

7. References 24 1. Introduction

This annual report on the seismicity of Norway and adjacent areas encompasses the time period January 1st - December 31st, 2008. The earthquake locations have been compiled from all available seismic stations operating on the Norwegian territory including the Arctic islands of Spitsbergen, Bjørnøya, Hopen and Jan Mayen. In addition, stations from neighbouring countries have been included for large or well- recorded events.

In Norway, the University of Bergen (UiB) operates the Norwegian National Seismic Network (NNSN) consisting of 33 seismic stations where 12 have broad band sensors. NORSAR operates 3 seismic arrays and one seismic station (Figure 1). Data from temporarily installed local networks are also included whenever data are made available. In addition to NNSN stations waveform data from other selected stations in Norway (operated by NORSAR), Finland, Denmark and Great Britain are transferred in real time and included in the NNSN database.

Phase data from arrays in Russia (Apatity), Finland (Finess), Sweden (Hagfors) and from stations operated by the British Geological Survey (BGS) are also included when available. All phase data are collected by UiB, and a monthly bulletin is prepared and distributed. All earthquakes with magnitude ≥ 2.0 on mainland Norway and M ≥ 3.0 around Jan Mayen and the Mid Atlantic ridge, are presented on the web pages and also e-mailed to European-Mediterranean Seismological Centre (EMSC). A brief overview of the events published in the monthly bulletins is given in this annual report. Macroseismic data for the largest felt earthquakes in Norway are collected, and macroseismic maps are presented.

Local, regional and teleseismic events that are detected by the UiB network are included. The merging of data between NORSAR and UiB is based on the following principles: i) All local and regional events recorded by NORSAR that are also detected by the NNSN network are included. ii) All local and regional events with local magnitude larger than 2.0 detected by NORSAR and not recorded by the NNSN are included. iii) All teleseismic events recorded by NORSAR and also detected by the NNSN are included. iv) All teleseismic events with NORSAR magnitude Mb5.0 are included.

Data from British Geological Survey (BGS) are included in the database in Bergen following similar criteria as mentioned above, however only events located in the prime area of interest, shown in Figure 1, are included.

Starting from 2008 the NNSN stations were upgraded to provide continuous data in real time. This has resulted in more effective monitoring of earthquake activity in the region.

Data availability to the public

All the data stored in the NNSN database is also available to the public via Internet, e-mail or manual request. The main web-portal for earthquake information is www.skjelv.no. It is possible to search interactively for specific data, display the data locally (waveforms and hypocenters) and then download the data. Data are processed daily and updated lists of events recorded by Norwegian stations are available soon after recording. All events with an estimated local magnitude  2.0 are processed daily and plotted on individual maps shown on the web pages. These pages are automatically updated with regular intervals.

Figure 1: Norwegian seismic stations. UiB operates the 33 stations (blue triangles) in the National Seismic Network (NNSN) and NORSAR operates the 3 arrays and the station JMIC (red triangles). Circles identify broad band stations.

2. Velocity models and magnitude relations

The velocity model used for locating all local and regional events, except for the local Jan Mayen events, is shown in Table 1 (Havskov and Bungum, 1987). Event locations are performed using the HYPOCENTER program (Lienert and Havskov, 1995) and all processing is performed using the SEISAN data analysis software (Havskov and Ottemöller, 1999).

Table 1: Velocity model used for locating all local and regional events, except for the local Jan Mayen events, (from Havskov and Bungum, 1987).

P-wave velocity Depth to layer (km/sec) interface (km) 6.2 0.0 6.6 12.0 7.1 23.0 8.05 31.0 8.25 50.0 8.5 80.0

Magnitudes are calculated from coda duration, amplitudes or seismic spectra. The coda magnitude relation was revised in 2006 (Havskov & Sørensen 2006). The coda wave magnitude scale (MC) is estimated through the relation

MC = -4.28 + 3.16  log10(T) +0.0003  D where T is the coda length in seconds and D is the epicentral distance in km. The new scale made MC more consistent with ML since MC in general is reduced. For this report all data are updated using the new magnitude scale. When instrument corrected ground amplitudes A (nm) are available, local magnitude ML is calculated using the equation given by Alsaker et al. (1991):

ML= 1.0  log(A) + 0.91  log(D) + 0.00087  D - 1.67 where D is the hypocentral distance in km.

The moment magnitude Mw is calculated from the seismic moment M0 using the relation (Kanamori, 1977)

Mw = 0.67  log(M0) – 6.06

The unit of M0 is Nm. The seismic moment is calculated from standard spectral analysis assuming the Brune model (Brune, 1970) and using the following parameters:

Density: 3.0 g/cm2 Q = 440  f 0.7 P-velocity = 6.2 km/s S velocity = 3.6 km/s

For more computational details, see Havskov and Ottemöller, (2003).

For the Jan Mayen area, a local velocity model (see Table 2) and coda magnitude scale is used (Andersen, 1987).

Table 2: Velocity model used for locating local Jan Mayen events.

P-wave velocity Depth to layer (km/sec) interface (km) 6.33 18 8.25 50

The coda magnitude scale for Jan Mayen which is used in this report is given by Havskov & Sørensen (2006). This scale was implemented in 2006 but all events used in this report are updated during April/May 2006.

MC = 3.27  log(T) 2.74 + 0.001  D where T is the coda duration and D is the epicentral distance in km.

The regional and teleseismic events recorded by the network are located using the global velocity model IASPEI91 (Kennett and Engdahl, 1991).

Body wave magnitude is calculated using the equation by Veith and Clawson (1972):

Mb = log(A/T) + Q(D,h)

Here h is the hypocentre depth (km), A is the amplitude (microns), T is period in seconds and Q(D,h) is a correction for distance and depth.

Surface wave magnitude Ms is calculated using the equation (Karnik et al., 1962):

Ms = log(A/T) + 1.66  log(D) + 3.3 where A is the amplitude (microns), T is period in seconds and D is the hypocentral distance in degrees.

Starting from January 2001, the European Macroseismic Scale, EMS98, (Grünthal, 1998) has been used. All macroseismic intensities mentioned in the text will refer to the EMS98 instead of the previously used Modified Mercalli Intensity scale. The two scales are very similar at the lower end of the scale for intensities less than VII.

3. Events recorded by the Norwegian stations

Based on the criteria mentioned in section 1 and above, a total of 4256 local and regional events, were detected by the Norwegian seismic stations during 2008. Of these local and regional events, 54% were large enough to be recorded by several stations and hence could be located reliably. The number of local/regional and teleseismic events, recorded per month in 2008 is shown in Figure 2. The average number of local and regional events recorded per month is 348. The number of recorded local/regional events is higher than in 2007 which can be explained by the Storfjorden earthquake (21st February) and its many aftershocks. This effect is clearly seen in Figure 2 were the number of recorded local/regional events in February through May is clearly above average for the rest of the year.

A total of 909 teleseismic events were recorded between January and December 2008, of which 95% were located. In addition to the locations determined at UiB, also preliminary locations published by the USGS (United States Geological Survey) based on the worldwide network are included in the UiB database whenever the earthquake is recorded with Norwegian stations. The monthly average of teleseismic earthquakes recorded by NNSN is 75.

600

500

400

300 Local/Regional Distant 200

100

0 JAN MAR MAY JUL SEP NOV

Figure 2: Monthly distribution of local/regional and distant events, recorded during 2008. The apparent increase in the number of local events during the period Jan – May is probably due to aftershocks of the Svalbard earthquake.

UiB, as an observatory in the global network of seismological observatories, reports as many secondary phases as possible from the teleseismic recordings. All events (teleseismic, regional and local) recorded from January to December 2008 with M  3 are plotted on Figure 3.

Monthly station recording statistics from January to December 2008 are given in Table 3. This table shows, for each station, the number of local events that were recorded only at one station, local events recorded on more than one station and recorded teleseismic events. It must be observed that Table 3 shows both earthquakes and explosions, and that the large number of detections at KTK mainly is due to explosions at the Kirruna/Malmberget mines in Sweden. The MOR station also records the Kirruna/Malmberget explosions but in addition the station also records a large number of local earthquakes. Since 2003 a new seismic station, STOK, was located close to the existing MOR station and in 2006 this is further extended by two more stations (FLOS and KONS). Therefore the number of recorded local earthquakes in this region is increased. During 2008 two new stations (HOMB and TBLU), both Broad Band stations, started operation and were added to the Norwegian National Seismic Network. Their location can be seen in Figure 1.

Figure 3: Epicentre distribution of earthquakes with M3.0, located by the Norwegian Seismic Network from January to December 2008. Teleseismic events recorded only by NORSAR have M5.0.

4. The seismicity of Norway and adjacent areas

A total of 2082 of the recorded events are located inside the NNSN prime area, 54N-82N and 15W-32E. During analysis and using the explosion filter (Ottemöller, 1995), 33% of these events were identified as probable explosions. Figure 4 shows all local/regional events in the prime area, analyzed and located during 2008.

Figure 4: Epicentre distribution of events analyzed and located from January through December 2008. Earthquakes are plotted in red and probable and known explosions in yellow. For station locations, see Figure 1. Table 3a: Monthly statistics of events recorded at each station for January-June 2008. Abbreviations are: LM = Number of local events recorded at more than one station, LS = Number of local events recorded at only one station and D = Number of teleseismic events. The stations TBLU and HOMB was installed in December 2008. JANUARY FEBRUARY MARCH MAY JUNE LM LS D LM LS D LM LS D APRILLM LS D LM LS D LM LS D STATIONASK 16 0 5 43 0 6 31 0 5 48 0 4 14 0 3 28 0 10 BER 7 0 14 4 0 16 9 0 20 9 0 14 10 0 30 8 0 35 BJO1 3 0 10 106 0 15 45 1 11 28 0 10 20 0 18 20 0 11 BLS5 20 0 6 31 0 14 26 0 9 50 0 11 40 0 4 30 1 13 DOMB 3 0 6 7 0 10 5 0 11 5 0 13 5 0 12 0 0 2 EGD 11 0 3 19 0 4 19 0 4 25 0 2 9 0 3 8 0 4 FLOS 53 0 3 44 0 2 56 0 2 91 0 4 35 0 5 35 0 7 FOO 0 0 0 21 1 11 26 0 14 33 0 19 16 0 32 18 0 27 HOMB ------HOPEN 15 7 0 234 80 1 161 34 1 41 0 0 62 11 1 28 4 4 HYA 20 4 1 38 1 8 44 2 6 59 1 9 25 0 7 21 0 10 JMI 11 0 0 9 0 0 9 0 0 17 0 0 23 0 0 18 0 0 JMIC 2 0 8 6 0 9 2 0 11 3 0 11 7 0 22 1 0 19 JNE 13 0 0 13 0 0 9 0 0 18 0 0 18 0 0 19 0 0 JNW 13 0 0 15 0 3 11 0 0 19 0 0 24 0 1 20 1 2 KBS 17 3 17 192 5 17 138 1 24 50 3 28 64 11 30 40 3 41 KMY 20 0 1 34 0 1 27 0 0 51 0 2 40 0 3 32 0 7 KONO 1 0 15 7 0 21 1 0 22 6 0 28 9 0 33 6 1 38 KONS 62 0 3 49 0 5 64 0 1 97 0 4 43 1 3 37 0 10 KTK1 33 3 11 26 1 14 24 5 17 38 2 12 18 0 20 4 0 21 LOF 39 1 6 33 2 10 26 2 11 118 2 12 45 2 20 19 1 12 MOL 3 0 4 9 0 14 7 0 19 7 0 14 11 0 17 4 0 15 MOR8 70 2 10 60 7 19 57 3 20 120 6 17 43 2 29 33 2 19 NSS 22 2 15 20 3 19 11 1 22 27 2 20 15 3 25 12 2 22 ODD1 21 0 7 40 0 12 31 0 11 47 0 10 10 0 0 19 0 7 OSL 0 0 5 1 0 9 0 0 16 2 0 18 4 0 23 0 0 15 RUND 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 5 0 1 SNART 15 0 6 27 1 5 17 0 4 30 0 5 24 0 9 9 0 10 STAV 3 0 2 8 0 3 2 0 2 3 0 0 5 0 3 1 0 5 STEI 42 3 4 24 0 5 18 0 9 107 0 3 34 0 5 14 0 7 STOK 70 0 7 52 0 14 66 1 14 96 0 16 42 0 15 30 0 11 SUE 9 0 1 11 0 0 15 0 3 19 0 2 11 0 5 15 0 5 TBLU ------TRO 25 0 17 21 0 22 16 0 28 32 0 29 11 0 44 3 0 41 NORSAR 19 0 47 19 0 64 14 0 70 23 0 77 35 0 108 18 0 82 ARCES 44 0 0 165 0 0 78 3 0 89 0 0 76 0 0 63 0 0 SPITS 16 0 0 139 0 0 50 0 0 47 0 0 34 0 0 26 0 0

Table 3b: Monthly statistics of events recorded at each station for July-December 2007. Abbreviations are: LM = Number of local events recorded at more than one station, LS = Number of local events recorded at only one station and D = Number of teleseismic events. JULY AUGUST SEPTEMBER NOVEMBER DECEMBER LM LS D LM LS D LM LS D OCTOBERLM LS D LM LS D LM LS D STATIONASK 25 0 17 22 0 2 60 0 13 40 0 8 30 0 13 27 0 13 BER 9 0 25 5 0 38 1 0 19 2 0 12 8 0 14 9 0 17 BJO1 11 0 15 8 0 23 8 0 10 7 1 13 7 0 8 4 0 9 BLS5 28 0 17 30 0 3 62 0 14 39 0 4 32 0 3 20 0 5 DOMB 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 2 EGD 8 0 3 9 0 0 10 0 4 21 0 4 12 0 3 0 0 0 FOO 21 0 23 18 0 37 24 0 22 30 0 13 12 0 15 17 0 16 FLOS 55 0 15 34 0 3 48 0 11 29 0 10 42 0 7 25 0 10 HOMB ------2 0 3 HOPEN 1 0 1 1 0 0 8 0 0 6 0 3 0 0 1 4 0 6 HYA 23 0 17 18 0 3 40 0 3 47 0 2 26 0 3 20 0 3 JMI 13 0 1 12 0 0 14 0 0 14 0 0 10 0 0 11 0 0 JMIC 11 0 20 8 0 34 17 0 15 5 0 11 9 0 9 8 0 2 JNE 24 0 1 18 0 0 19 0 0 18 0 0 15 0 0 14 0 0 JNW 24 0 3 18 0 0 23 2 0 18 0 1 18 0 0 16 0 0 KBS 24 3 31 23 4 47 24 5 20 24 1 21 29 0 18 22 4 24 KMY 29 0 13 22 0 0 54 0 1 30 0 0 31 0 1 22 0 3 KONO 1 0 26 4 0 44 3 0 15 4 0 18 10 0 22 5 0 26 KONS 62 0 16 42 0 6 51 0 10 31 0 4 32 0 3 4 0 3 KTK1 17 1 23 18 0 39 31 5 40 20 2 29 22 4 35 35 3 42 LOF 55 5 19 16 1 14 23 1 16 6 0 7 4 0 5 6 0 7 MOL 4 0 13 4 0 17 5 0 9 5 0 13 2 0 12 2 0 11 MOR8 71 3 29 45 0 27 50 6 31 34 1 23 43 4 16 35 1 29 NSS 16 2 24 19 0 37 22 0 23 14 0 17 17 0 16 9 0 21 ODD1 20 0 15 20 0 0 50 0 11 19 0 2 27 0 7 18 0 18 OSL 0 0 18 1 0 23 1 0 22 0 0 6 0 0 12 1 0 8 RUND 5 0 3 15 0 2 51 0 14 33 0 9 28 0 13 21 0 11 SNART 5 0 4 20 0 9 41 0 7 20 0 8 26 0 14 19 0 18 STAV 0 0 13 1 0 0 1 0 1 2 0 1 2 0 3 0 0 1 STEI 49 1 12 11 0 1 21 0 11 6 0 11 7 0 23 11 0 19 STOK 52 0 11 34 0 4 43 0 13 32 0 17 42 0 22 24 0 17 SUE 16 0 9 12 0 0 13 0 6 16 0 1 12 0 2 7 0 0 TBLU ------1 0 3 TRO 16 1 34 16 0 51 24 0 41 7 0 26 8 0 30 13 0 44 NORSAR 31 0 79 21 0 70 32 0 67 23 0 62 22 0 63 17 0 79 ARCES 74 0 0 63 1 0 49 0 0 76 0 0 69 1 0 47 0 0 SPITS 21 0 0 17 0 0 8 0 0 28 0 5 37 0 24 28 0 34 Figure 5 and Table 4 show the 141 local and regional events, located in the prime area, with one of the calculated magnitudes greater than or equal to 3.0. Among these, 40 are located in the vicinity of the Jan Mayen Island. Depth is checked for the earthquakes with magnitude equal or above 3.0.

It should be emphasized that it is often difficult to get a good magnitude estimate for the earthquakes located on the oceanic ridge in the Norwegian sea, since distances are too large to compute a proper ML, too short for Mb and coda magnitudes for these locations are often unreliable. Most of the recorded earthquakes in this area have magnitudes above 3.0 if they are recorded on Norwegian mainland stations.

Figure 5: Epicentre distribution of located events with one of the calculated magnitudes above or equal to 3.0. All earthquakes are listed in Table 2. For station location, see Figure 1.

Table 4: Local and regional events in prime area with any magnitude above or equal to 3.0 for the time period January through December 2008. Only magnitudes reported by the University of Bergen are included. In cases where all BER magnitudes are below 3 but the event still is included in the list, NORSAR has reported a magnitude of 3.0 or larger. Abbreviations are: HR = hour (UTC), MM = minutes, Sec = seconds, L = distance identification (L=local, R=regional, D=teleseismic), Latitud = latitude, Longitud = longitude, Depth = focal depth (km), F = fixed depth, AGA = agency (BER=Bergen), NST = number of stations, RMS = root mean square of the travel-time residuals, Mc = coda magnitude, Ml = local magnitude and Mw = moment magnitude.

Year Date HRMM Sec L Latitud Longitud Depth FF AGA NST RMS Mc Ml Mw Mb Ms 2008 1 3 0050 26.2 L 78.355 8.112 10.0 F BER 3 0.7 2.1 3.3 2008 115 0029 1.7 L 71.390 -6.933 10.0 F BER 3 0.3 2.3 3.1 2.9 2008 118 1902 10.8 L 71.003 -7.410 10.0 F BER 5 0.4 2.7 3.5 3.2 2008 122 0510 56.5 L 74.266 14.461 10.0 F BER 11 1.2 2.7 2.3 2008 2 4 0930 16.0 L 76.143 26.527 15.0 F BER 4 0.9 2.8 3.3 2008 2 4 2158 47.7 L 76.277 23.668 15.0 F BER 9 1.5 2.4 3.2 3.4 2008 212 1321 55.6 L 78.019 8.332 15.0 F BER 2 0.5 2.5 2.9 2008 221 0246 19.3 L 77.243 20.261 15.0 F BER 31 2.9 5.7 6.0 5.7 5.9 2008 221 0253 57.5 L 77.135 18.265 15.0 F BER 5 0.6 3.4 3.4 2008 221 0306 32.7 L 77.062 19.530 15.0 F BER 5 0.8 3.1 3.2 2008 221 0308 54.0 L 77.037 18.928 15.0 F BER 4 0.7 3.0 3.0 2008 221 0324 8.0 L 77.100 19.977 15.0 F BER 4 1.1 3.4 2008 221 0326 3.1 L 77.033 19.242 15.0 F BER 5 0.9 2.1 3.0 2008 221 0332 51.3 L 77.113 18.932 15.0 F BER 7 0.7 2.2 3.3 3.2 2008 221 0350 59.8 L 77.074 19.149 15.0 F BER 5 1.1 2.1 3.0 2.8 2008 221 0356 26.4 L 77.586 19.988 15.0 F BER 8 0.9 3.1 3.7 3.3 2008 221 0409 26.6 L 77.333 19.545 15.0 F BER 10 1.1 2.8 3.6 3.6 4.2 2008 221 0413 13.6 L 76.777 19.374 15.0 F BER 5 0.8 2.3 3.0 2.8 2008 221 0427 19.0 L 77.431 19.419 15.0 F BER 5 0.7 2.0 3.2 3.2 2008 221 0515 12.9 L 77.039 19.131 15.0 F BER 11 1.1 2.6 3.7 3.7 4.4 2008 221 0745 24.6 L 77.121 18.943 15.0 F BER 5 1.0 2.4 3.0 3.0 2008 221 1155 49.9 L 77.086 18.755 15.0 F BER 5 0.8 2.6 3.3 3.4 2008 221 1220 12.0 L 77.047 19.031 15.0 F BER 6 0.7 2.1 3.3 3.2 2008 221 2135 29.3 L 77.085 18.826 15.0 F BER 5 0.8 3.0 3.0 2008 221 2228 48.9 L 77.148 19.394 15.0 F BER 5 1.1 2.3 3.1 3.0 2008 221 2252 40.9 L 77.035 19.403 15.0 F BER 13 1.1 2.5 3.8 4.0 4.1 2008 222 0021 24.5 L 77.074 19.240 15.0 F BER 9 0.7 2.5 4.2 4.1 2008 222 0219 30.0 L 77.194 18.785 15.0 F BER 8 0.8 2.1 3.7 3.6 2008 222 0451 56.4 L 77.093 19.225 15.0 F BER 6 0.7 2.3 3.6 3.6 2008 222 0630 30.4 L 77.068 19.512 15.0 F BER 4 0.5 3.1 3.3 3.3 2008 222 0647 15.4 L 77.067 19.172 15.0 F BER 5 0.8 2.2 3.2 3.0 2008 223 0531 6.5 L 77.151 19.219 15.0 F BER 5 0.6 2.6 3.4 2008 223 0900 16.1 L 77.196 19.446 15.0 F BER 7 1.1 3.6 3.9 4.1 4.2 2008 224 0042 5.1 L 77.163 19.467 15.0 F BER 5 0.5 2.7 3.0 3.0 2008 224 0320 16.0 L 77.153 19.139 15.0 F BER 5 0.9 2.0 3.4 3.5 2008 224 0323 56.1 L 77.564 18.080 15.0 F BER 9 1.1 3.8 3.6 2008 224 0905 16.9 L 77.076 19.149 15.0 F BER 8 0.9 2.4 3.5 3.3 2008 224 0928 33.4 L 71.324 -6.513 10.0 F BER 3 0.1 2.6 3.0 2.8 2008 224 1048 45.0 L 77.032 19.199 15.0 F BER 8 0.8 2.6 3.6 3.3 2008 224 1417 6.0 L 77.030 19.121 15.0 F BER 5 0.7 2.0 3.2 3.2 2008 225 1502 16.0 L 77.147 19.369 15.0 F BER 6 0.7 2.5 3.2 3.2 2008 226 1102 20.3 L 77.181 19.458 15.0 F BER 6 0.9 2.5 3.3 3.3 2008 229 0816 6.6 L 77.315 20.413 15.0 F BER 18 2.3 3.9 4.1 4.2 2008 3 2 0657 47.9 L 77.024 19.237 15.0 F BER 10 1.1 2.6 3.4 3.7 2008 3 3 1859 35.5 L 79.210 4.866 10.0 F BER 5 1.7 2.9 3.1 3.1 2008 3 4 1255 24.6 L 77.034 19.169 15.0 F BER 10 1.0 2.4 3.8 3.5 2008 3 7 1007 52.1 L 77.089 19.430 15.0 F BER 5 0.7 2.3 3.1 3.1 2008 3 8 1656 30.2 L 77.116 19.047 15.0 F BER 6 0.4 2.8 3.1 3.4 2008 3 9 0948 44.7 L 79.171 4.283 10.0 F BER 5 1.4 3.0 3.1 2008 3 9 1953 13.8 L 77.131 18.998 15.0 F BER 5 0.4 2.3 3.1 3.4 2008 310 0317 20.7 L 77.275 18.852 15.0 F BER 7 1.2 2.9 3.2 3.2 2008 311 0605 15.0 L 77.188 19.268 15.0 F BER 7 1.0 2.6 3.2 3.4 2008 311 1407 26.2 L 77.083 19.026 15.0 F BER 7 1.0 2.5 3.5 3.5 2008 312 1314 49.1 L 77.255 18.747 15.0 F BER 6 1.0 2.3 2.9 3.0 2008 312 1833 43.4 L 77.207 18.600 15.0 F BER 6 1.2 2.4 3.1 3.2 2008 323 1229 38.1 L 77.183 19.307 15.0 F BER 5 1.0 2.2 3.1 3.2 2008 324 1828 20.0 L 80.895 17.527 15.0 F BER 10 1.4 3.2 3.8 2008 331 0148 4.9 L 71.336 -11.146 10.0 F BER 10 2.3 3.9 3.4 3.6 4.3 2008 331 1703 50.6 L 80.487 12.743 10.0 F BER 3 0.6 3.1 3.3 4.3 2008 4 7 2351 19.6 L 76.622 9.168 15.0 F BER 9 1.2 2.5 3.1 2.8 2008 4 8 0332 59.9 L 77.100 19.092 15.0 F BER 7 1.1 2.5 3.7 3.6 2008 4 9 0122 48.1 L 70.898 -7.472 10.0 F BER 12 1.3 3.3 3.1 3.6 2008 410 0620 3.6 L 77.118 19.636 15.0 F BER 14 1.4 3.2 4.3 4.3 2008 411 0602 56.5 L 67.848 15.154 5.0 F BER 12 1.2 3.2 3.4 2008 413 0346 9.3 L 77.103 18.737 15.0 F BER 6 0.7 2.6 3.1 3.0 2008 418 2239 38.2 L 77.130 18.909 15.0 F BER 4 1.5 3.2 3.0 2008 424 1714 56.6 L 69.685 18.466 15.0 F BER 12 1.8 3.2 2.7 3.0 2008 425 0453 18.7 L 69.669 18.455 15.0 F BER 12 1.5 3.4 2.9 3.1 2008 425 2228 8.2 L 77.063 18.984 15.0 F BER 6 0.8 2.3 3.3 3.2 2008 5 1 0805 54.2 L 71.319 -8.786 10.0 F BER 3 0.2 2.7 3.4 2008 5 5 0435 51.1 L 71.169 -7.702 15.0 F BER 3 0.0 2.6 3.0 3.1 2008 5 6 0450 14.3 L 71.772 -11.904 10.0 F BER 3 0.1 3.5 3.4 2008 5 6 0500 23.6 L 71.547 -12.579 10.0 F BER 3 0.1 3.5 3.3 3.2 2008 5 6 1951 12.6 L 71.408 -12.462 10.0 F BER 10 2.9 3.6 3.6 2008 5 6 2055 44.1 L 71.870 -12.005 10.0 F BER 4 0.5 4.1 3.4 3.6 2008 5 6 2338 4.8 L 70.743 -12.973 10.0 F BER 3 0.6 2.7 3.0 2008 5 6 2348 30.7 L 77.143 18.895 15.0 F BER 6 0.8 3.2 2008 5 7 1643 51.2 L 71.407 -12.937 10.0 F BER 10 1.3 3.7 4.8 2008 5 8 0820 44.1 L 71.912 -12.058 10.0 F BER 3 0.3 2.9 3.0 2.8 2008 5 8 2239 14.7 L 77.050 19.092 15.0 F BER 8 1.4 2.6 3.4 3.5 2008 516 0033 51.4 L 77.058 19.096 15.0 F BER 4 0.4 2.2 3.0 3.1 2008 518 0213 41.1 L 77.154 19.304 15.0 F BER 7 1.0 3.1 3.3 2008 521 1207 45.4 L 77.074 19.162 15.0 F BER 5 1.1 2.6 3.3 2008 524 0818 16.4 L 71.411 -3.955 10.0 F BER 21 1.3 2.3 2.9 3.0 2008 6 1 0624 37.7 L 79.792 4.472 10.0 F BER 12 1.6 3.6 3.3 2008 6 3 2359 6.0 L 80.884 -0.850 10.0 F BER 3 1.1 3.1 2.6 2008 6 4 2125 43.8 L 70.962 -6.834 10.0 F BER 24 1.7 3.3 3.8 2008 6 4 2329 24.9 L 71.000 -6.740 10.0 F BER 3 0.1 2.6 3.0 3.0 2008 611 1252 16.8 L 77.156 19.060 15.0 F BER 5 1.0 3.1 3.1 2008 617 0911 51.4 L 69.811 29.899 15.0 F BER 20 1.2 3.4 2.3 2.6 2008 7 6 1721 25.2 L 71.210 -6.238 10.0 F BER 3 0.1 3.0 2.7 3.0 2008 710 1036 13.1 L 71.290 -6.644 10.0 F BER 3 0.1 3.0 2.6 2.7 2008 716 1037 36.7 L 71.336 -9.222 10.0 F BER 3 0.1 3.0 3.1 2.9 2008 730 1406 26.7 L 78.564 22.498 15.0 F BER 12 1.5 3.3 4.0 2008 731 0128 1.0 L 74.286 13.264 10.0 F BER 8 1.0 2.6 2.4 2008 8 2 1625 42.0 L 76.902 20.360 15.0 F BER 12 1.1 2.2 3.8 3.7 2008 8 3 2014 34.8 L 70.765 -7.017 10.0 F BER 9 1.2 3.4 3.9 3.7 2008 8 8 0421 19.8 L 79.916 4.139 10.0 F BER 3 0.7 2.9 3.3 2008 8 9 0350 37.5 L 78.419 7.574 10.0 F BER 2 0.1 1.7 1.8 2008 8 9 0725 19.0 L 71.035 -7.360 10.0 F BER 3 0.1 2.9 3.2 3.0 2008 814 0718 21.8 L 79.609 4.766 10.0 F BER 10 1.9 3.7 3.5 2008 818 0100 8.0 L 70.970 -7.238 10.0 F BER 3 0.2 2.7 3.2 3.0 2008 824 1021 56.4 L 77.013 19.150 15.0 F BER 5 0.7 2.8 3.4 3.4 2008 831 0316 47.4 L 71.258 -6.498 10.0 F BER 3 0.3 2.9 3.3 3.1 2008 831 1153 42.6 L 70.609 -7.958 10.0 F BER 3 0.5 2.6 3.1 2008 9 8 2117 18.1 L 72.253 1.466 10.0 F BER 20 1.4 3.1 3.2 2008 9 9 0422 44.0 L 80.708 -2.187 10.0 F BER 8 1.3 3.9 2.9 2008 920 0440 38.5 L 78.804 -0.097 10.0 F BER 5 1.8 3.1 2008 925 1534 13.2 L 77.304 19.424 15.0 F BER 5 0.9 2.7 3.5 3.6 2008 927 0220 13.4 L 65.951 30.034 13.0 F BER 17 1.3 3.4 2.4 2008 928 1952 25.4 L 71.548 -4.724 10.0 F BER 16 1.2 2.8 3.4 5.0 2008 928 2220 18.6 L 71.277 -4.321 10.0 F BER 26 0.9 3.7 3.7 5.3 5.1 2008 928 2313 6.6 L 71.515 -4.685 10.0 F BER 11 0.8 3.1 2008 929 0349 57.1 L 77.478 24.352 15.0 F BER 4 0.8 2.5 3.5 2008 929 1103 54.6 L 71.491 -4.702 10.0 F BER 13 1.1 3.0 3.3 4.8 4.0 2008 929 1916 45.1 L 71.581 -4.594 10.0 F BER 22 1.0 2.6 3.7 3.7 4.7 4.2 2008 929 1920 21.0 L 71.513 -4.572 10.0 F BER 15 0.8 2.9 3.2 5.0 2008 10 4 0212 37.5 L 80.095 20.887 15.0 F BER 4 1.1 3.1 3.0 2008 1010 0428 39.7 L 56.832 -5.494 10.0 F BER 40 1.2 3.2 3.1 2008 1014 0223 44.5 L 62.326 1.663 10.0 F BER 39 1.3 3.0 3.2 3.0 2008 1014 1647 42.1 L 69.762 30.725 10.0 F BER 12 1.6 3.4 3.1 3.0 2008 1016 1932 0.4 L 64.345 20.825 15.0 F BER 10 1.5 3.5 2.7 3.0 2008 1018 1938 44.9 L 71.021 -6.671 10.0 F BER 3 0.1 2.6 3.1 3.0 2008 1026 1044 39.9 L 79.577 4.748 10.0 F BER 3 1.0 1.9 3.0 2008 11 4 0019 44.7 L 77.292 19.518 15.0 F BER 4 0.9 3.0 2008 11 4 0213 3.1 L 73.367 14.155 10.0 F BER 9 1.2 3.1 2.4 2.4 2008 11 7 2017 39.7 L 71.339 -12.157 10.0 F BER 13 1.4 4.1 3.7 4.1 2008 11 7 2113 15.7 L 71.712 -11.588 10.0 F BER 7 0.5 3.4 3.5 3.3 2008 11 7 2140 54.6 L 71.621 -12.112 10.0 F BER 18 1.6 4.9 4.0 2008 11 8 2121 54.9 L 71.158 -6.575 10.0 F BER 3 0.1 3.0 3.6 3.4 2008 1117 0551 41.5 L 80.325 6.692 10.0 F BER 3 1.1 2.1 2.7 2008 1120 0118 42.9 L 62.521 18.065 15.0 F BER 12 1.1 3.2 2.6 2.9 2008 1120 2344 2.0 L 77.058 19.536 15.0 F BER 3 0.9 2.6 3.1 2008 1128 0329 6.1 L 77.056 19.883 15.0 F BER 5 0.9 2.9 3.3 2008 1216 0520 3.0 L 55.643 13.636 10.0 F BER 32 1.8 4.1 4.6 4.3 2008 1216 1032 0.4 L 71.179 -7.824 10.0 F BER 3 0.1 2.1 3.1 2008 1217 0632 36.4 L 71.058 -7.723 10.0 F BER 13 1.2 3.7 3.6 2008 1218 1253 20.2 L 71.692 -11.462 10.0 F BER 11 0.7 3.7 3.5 2008 1220 0006 52.8 L 70.833 -7.192 10.0 F BER 24 1.7 2.9 3.5 2008 1222 0749 40.7 L 76.807 15.441 15.0 F BER 5 1.0 2.4 3.0 2008 1225 0414 25.5 L 71.586 -2.819 10.0 F BER 19 1.2 3.0 The largest local or regional earthquake in 2008, recorded on Norwegian stations and within the prime area, occurred on February 21st at 02:46 (UTC) in Storfjorden southwest of Spitsbergen. The earthquake had a magnitude of MW=6.0 (BER) and was strongly felt in Longyearbyen. Among the largest earthquakes in the vicinity of the Norwegian mainland is the earthquake located in Varangerfjorden, occurring on 14th October at 16:47 with a magnitude of ML=3.4.

Figure 6: Seismograms for the earthquake on February 21st, 2008 at 02:46(UTC). This earthquake is located in Storfjorden, Svalbard. The seismograms are not filtered. The horizontal time scale is minutes, first marking at 02:46 (UTC). The station abbreviations are: KONO: Kongsberg, KBS: Kings bay, HOPEN: Hopen island, BJO: Bjørnøya, TRO: Tromsø, LOF: Lofoten, STEI: Steigen, MOR: Mo i Rana, JMI and JNW: Jan Mayen, KONS: Konsvik, STOK: Stokkvågen, NSS: Namsos, MOL: Molde, DOMB: Dombås, FOO: Florø, HYA: Hyanger, ASK: Askøy, BER: Bergen, EGD: Espegrend, ODD: Odda, BLS: Blåsjø, SNART: Snartemo and KMY: Karmøy.

The magnitude 6 earthquake in Storfjorden, Svalbard.

st At 02:46 (UTC) on 21 February 2008 a magnitude 6.0 (MW) earthquake occurred in Storfjorden, Svalbard, approximately 155 km south east of Longyearbyen. The earthquake was strongly felt in Longyearbyen and is the largest intraplate earthquake recorded on Norwegian territory. The mainshock was followed by a large number of aftershocks, which is still ongoing.

st Figure 7. Aftershocks of the Svalbard earthquake (MW=6.0) of February 21 , 2008. The mainshock is shown in blue quadrangle.

During 2008, 296 aftershocks were located to the Storfjorden area as seen in Figure 7. Due to the many aftershocks recorded on the Hopen and KBS stations, a high number of earthquakes are still not processed and located. The monthly distribution of the located earthquakes are presented in Figure 8.

140 120 100 80 Number of located 60 earthquakes 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12

Figure 8. Monthly distribution of aftershocks of the Svalbard earthquake.

On 30th September, 2008, an internet connection via satellite was obtained at Hopen and data recorded at the seismic station on the island could from then on be transferred in real time. It is now possible to integrate phase readings from the HOPEN station with the data collected from other stations and the location of the earthquakes in the Storfjorden area are more accurate. Prior to the satellite communication, seismic data were received on memory sticks often with months delay. A study of the Storfjorden earthquake is presented in Pirli et.al. (in prep).

Earthquake recordings in the Stokkvågen area

The network around Stokkvågen continued operation in 2008. The seismic activity is approximately the same as for 2007 but reduced compared to 2006. During 2008, 204 seismic events were located in the area shown on Figure 9. There is a renewed research interest in the area and independent funding might be needed for additional monitoring of seismicity and crustal motions.

Figure 9: Events located in the Stokkvågen area during 2008.

Earthquake recordings in the Steigen area

A new seismic station (STEI) was installed in June 2007, in the Steigen area in Nordland. This seismic station is recording small local earthquakes and also the larger earthquakes occurring offshore Lofoten. During 2008 a total of 179 small local events was recorded by STEI and located to the area shown in Figure 10.

Figure 10. Events located in the Steigen area during 2008. LEINS is a portable station temporary used in autumn 2007.

It is evident that the distribution of epicentres follows a NE-trend, which is known to coincide with a previously known zone of weakness (Atakan et. al. 1994). However, the activity now seems to be more concentrated in the NE when compared to the 1993 earthquake swarm.

80 70 60 Number of located events 50 during 2007 40 Number of located events 30 during 2008

earthquakes 20 Number of felt earthquakes

Number of located located of Number 10 0

Month of year

Figure 11. Events located in the Steigen area, during 2007 and 2008.

The monthly number of located earthquakes within the area defined in Figure 10, are presented in Figure 11. The number increases in November 2007 and reaches a maximum in December 2007. During the first 7 months of 2008 the number of events decreases with two local highs in April and July. Several of these earthquakes were reported felt by the local population, 4 in 2007 and 6 during 2008. The data presented are not filtered for explosions and some might be manmade events.

Jan Mayen

The Jan Mayen Island is located in an active tectonic area with two major structures, the Mid Atlantic ridge and the Jan Mayen fracture zone, interacting in the vicinity of the island. Due to both tectonic and magmatic activity in the area, the number of recorded earthquakes is higher than in other areas covered by Norwegian seismic stations. During 2008 a total of 197 earthquakes were located as seen on Figure 12 and of these, 40 were calculated to have a magnitude equal to or above 3.0. The largest earthquake in the Jan Mayen region occurred August 3rd at 20:14 (UTC). This earthquake was located to 70.9N and 6.8W with magnitude 3.9.

Figure 12: Earthquakes located in the vicinity of the Jan Mayen Island during 2008.

The number of recorded earthquakes in the Jan Mayen area has varied over the last years, see Figure 13. The number of relative strong earthquakes show smaller time variation than smaller earthquakes. The apparent increase in 2004 and 2005 is due to the M=6.0 earthquake in 2004 and its aftershocks (Sørensen et al., 2007).

600 500

400 Total number of recorded 300 earthquakes 200 Number og events with magnitude above 3.0 100 0 2001 2003 2005 2007

Figure 13: Yearly distribution of earthquakes located in the Jan Mayen area.

5. Felt earthquakes

From 2006 it is possible to report felt earthquakes using the internet. On the site www.skjelv.no., questionnaires are available for the public. In total, 18 earthquakes were reported felt during 2008 (see Table 5 and Figure 14).

Table 5: Earthquakes reported felt in the BER database in 2008. Abbreviations are: Mc = coda magnitude, ML = local magnitude and Mw = moment magnitude, Q: questionnaires sent (Y/N), W: questionnaires received on web.

Time Max. Instrumental Nr Date (UTC) Intensity Magnitude (BER) epicentre location Q W (MMI) 1 27.01.08 13:21 III ML=2.1,ML=2.3 56.98N / 05.60W - - (BGS) 2 30.01.08 07:34 III Mc=2.2, ML=1.7 67.88N / 15.09E N N 3 30.01.08 07:39 III Mc=2.6, ML=2.7 67.88N / 15.01E N N 4 12.02.08 06:35 III Mc=2.8, ML=2.5 67.84N / 15.23E N N 5 21.02.08 02:42 III ML=2.1, ML=2.4 55.14N / 07.47W - - (BGS) 6 21.02.08 02:46 VI ML=5.7, MW=6.0 77.24N / 20.26E N Y 7 10.04.08 06:20 III Mc=3.2, ML=4.3, 77.11N / 19.45E N N MW=4.3 8 11.04.08 06:02 IV ML=3.2, MW=3.4 67.83N / 15.15E N Y 9 11.04.08 06:04 III ML=2.6 67.95N / 15.36E N N 10 24.04.08 17:14 III Mc=3.2, ML=2.7, 69.69N / 18.45E N N MW=3.0 11 25.04.08 04:53 III Mc=3.4, ML=2.9, 69.67N / 18.45E N N MW=3.1 12 15.05.08 09:05 V Mc=2.4, ML=2.0 66.82N / 13.78E N Y 13 25.05.08 01:10 V Mc=2.8, ML=2.6 60.07N / 10.73E N Y 14 29.05.08 16:22 V ML=2.6 69.69N / 30.06E N Y 15 07.07.08 22:42 III Mc=2.4, ML=2.1 67.83N / 15.19E N N 16 14.10.08 16:47 III Mc=3.4, ML=3.1, 69.76N / 30.72E N Y MW=3.0 17 22.10.08 17:02 III Mc=2.2, ML=2.5 60.69N / 04.53E N N 18 03.11.08 09:53 III ML=2.4, ML=2.5 56.37N / 05.50W - - (BGS)

Figure 14: Location of the 18 earthquakes reported felt during 2008.

6. Use of NNSN data during 2008

Data collected on Norwegian seismic stations are made available through the Internet and is provided on request to interested parties. Therefore it is difficult to get a comprehensive overview on the use and all publication based on Norwegian data.

Publications and reports

Atakan, K. 2008. Sichuan earthquake of 12 May 2008 (M=7.9) in central China: Why it happended? GEO-Magasin, 11.Årgang, Nr.4 – 2008, 50-52. Chatelain, J-L., Guillier, B., Cara, F., Duval, A-M., Atakan, K., Bard, P-Y., and the WP02 SESAME Team. 2008. Evaluation of the influence of experimental conditions on H/V results from ambient noise recordings. Bulletin of Earthquake Engineering, Vol. 6, Issue 1, 33-74, doi: 10.1007/s10518-007-9040-7. Gibbons, Steven, J., Frode Ringdal, Tormod Kværna, (2008), Detection and characterization of seismic phases using continuous spectral estimation on incoherent and partially coherent arrays. Geophysical Journal International, Vol. 172, No. 1. pp. 405-421. Guillier, B., Atakan, K., Chatelain, J-L., Havskov, J., Ohrnberger, M., Cara, F., Duval, A-M., Zacharapoulos, S., Teves-Costa, P., and the SESAME Team. 2008. Influence of instruments on H/V spectral ratios of ambient vibrations. Bulletin of Earthquake Engineering, Vol. 6, Issue 1, 3-31, doi: 10.1007/s10518-007-9039-0. Haghshenas, Bard, P-Y., Theodulidis, N. and the SESAME WP04 Team (K. Atakan, F. Cara, C. Cornou, G. Cultrera, G. Di Giulio, P. Dimitriu, D. Fäh, R. de Franco, A. Marcellini, M. Pagani, A. Rovelli, A. Savvaidis, A.Tento, S. Vidal and S. Zacharopoulos). 2008. Empirical evaluation of the microtremor H/V spectral ratio. Bulletin of Earthquake Engineering, Vol. 6, Issue 1, 75-108, doi: 10.1007/s10518-007-9058-x. Pirli, M., & J. Schweitzer (2008), Overview of NORSAR system response. Semiannual Technical Summary, 1 July – 31 December 2007, NORSAR Scientific Report 1–2008, 64-77, Kjeller, Norway, February 2008 Pirli, M. & J. Schweitzer (2008), Continued overview of NORSAR system response: the NORES and ARCES arrays. Semiannual Technical Summary, 1 January – 30 June 2008, NORSAR Scientific Report 2–2008, 68-93, Kjeller, Norway, August 2008 Ringdal, R., T. Kværna, S. Mykkeltveit, S. Gibbons & J. Schweitzer (2008), Basic research on seismic and infrasonic monitoring of the European Arctic. Semiannual Technical Summary, 1 July – 31 December 2007, NORSAR Scientific Report 1–2008, 28-40, Kjeller, Norway, February 2008 Ringdal, F., T. Kværna, S. Mykkeltveit, S. Gibbons & J. Schweitzer (2008), Basic research on seismic and infrasonic monitoring of the European Arctic. 30th Seismic Research Review: Ground-based nuclear explosion monitoring technologies. Portsmouth, Virginia, September 23 – 25, 2008, LA-UR-08-05261, Proceedings, CD Version file 7 – 06, Volume 2, 968-977 Ringdal, F., S. J. Gibbons, D. B. Harris (2008), Adaptive Waveform Correlation Detectors for Arrays: Algorithms for Autonomous Calibration. Proceedings of the 30th Monitoring Research Review, Ground-Based Nuclear Explosion Monitoring Technologies. Portsmouth, Virginia, September 23-25, 2008. LA-UR-08-05261 (2008), pp. 465-474. Ringdal, F., D. B. Harris, T. Kvaerna, S. J. Gibbons, (2008), Expanding Coherent Array Processing to Larger Apertures Using Empirical Matched Field Processing. Proceedings of the 30th Monitoring Research Review, Ground-Based Nuclear Explosion Monitoring Technologies. Portsmouth, Virginia, September 23-25, 2008. LA-UR-08-05261 (2008), pp. 455-464. Schweitzer, J. & The IPY Project Consortium Members (2008), The International Polar Year 2007-2008 Project “The Dynamic Continental Margin between the Mid-Atlantic-Ridge System (Mohn’s Ridge, Knipovich Ridge) and the Bear Island Region”. Semiannual Technical Summary, 1 July – 31 December 2007, NORSAR Scientific Report 1–2008, 53-63, Kjeller, Norway, February 2008. Selby, N.D. (2008), Application of a Generalized F Detector at a Seismometer Array. Bulletin of the Seismological Society of America, Vol. 98, No. 5., pp. 2469-2481. Weidle, Ch., V. Maupin, J. Ritter, T. Kværna, J. Schweitzer, N. Balling, H. Thybo & J. I. Faleide (2008), Mantle investigations of Norwegian Uplift Structure (MAGNUS) - a temporary network in southern Norway. Geophysical Research Abstracts, 10, EGU2008-A-06580, 2008 (abstract), SRef-ID: 1607-7962/gra/EGU2008-A-06580

NNSN related Talks & Poster 2008 Atakan, K. 2008. Hvor slår det neste store jordskjelvet til? Popular scientific presentation (in Norwegian). VilVite Science Center, Bergen, Norway, 3 February 2008. Atakan, K. 2008. Earthquake monitoring in the Arctic: Norwegian, Greenland and Barents Seas. MARUM International Workshop on “Hydroacoustic Monitoring of Glacier Activity in Greenland”, University of Bremen, Bremen, Germany, 21-22 April 2008. Atakan, K. 2008. The need for standardized approach for estimating the local site effects based on ambient noise recordings. Symposium on Geophysics and Remote Sensing in Determination of Near Surface Structures (GARS2008), Izmir, Turkey, 30 April – 2 May 2008. Atakan, K., Ottemöller, L., Raeesi, M., and Havskov, J. 2008. Two recent earthquakes: linking long-term deformation with present day seismicity and hazard. Nordic Seismology Seminar, Oslo, Norway, 4-6 June 2008. Bjerrum, L.W., Raeesi, M., and Atakan, K. 2008. Simulated ground motion distribution during the Wenchuan (China) earthquake of 12 May 2008 (M=7.9) using a slip model based on waveform inversion. 14th World Conference in earthquake Engineering. Beijing, China, 12-17 October 2008. Pirli, M., J. Schweitzer, B. Paulsen and T. Kværna (2008), Preliminary analysis of the Storfjorden, Svalbard, 21st February 2008 earthquake and its aftershock sequence. Abstract presented at the 39th Nordic Seismology Seminar, Oslo, Norway, June 2008. Pirli, M., S.J. Gibbons, H. Bungum, J. Schweitzer, T. Kværna, K. Atakan, J. Havskov, L. Ottemöller, M. Raeesi, A. Guterch, W. Debski, P. Wiejacz, P. Sawicki and B. Paulsen (2008), The 21st February 2008 Svalbard earthquake: Relative location of the aftershock sequence and seismotectonic interpretation. Abstract presented at the 33rd International Geological Congress, Oslo, Norway, August 2008. Pirli, M., M. Raeesi, S.J. Gibbons, L. Ottemöller, J. Schweitzer, K. Atakan, B. Paulsen, A. Guterch, J. Havskov, H. Bungum, M. Sawicki, T. Kværna, W. Debski and P. Wiejacz (2008), The 21st February 2008 Svalbard earthquake: analysis, location and seismotectonic interpretation of the aftershock sequence. Abstract presented at the XXXI General Assembly of the European Seismological Commission, Hersonissos, Crete, Greece, September 2008. Raeesi, M., Havskov, J., and Atakan, K. 2008. The mid-Atlantic ridge, a look through global travel-time tomography. Nordic Seismology Seminar, Oslo, Norway, 4-6 June 2008. Roth, M. and J. Fyen, (2008). Status of the NORSAR network. 39th Nordic Seismology Seminar, June 4-6, 2008, Oslo Schweitzer, J., A. Guterch, F. Krüger, M. Schmidt-Aursch & Bear Island Project Group (2008), The IPY project “The Dynamic Continental Margin between the Mid-Atlantic-Ridge System (Mohns Ridge, Knipovich Ridge) and the Bear Island Region”. 68. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Freiberg 3. – 6. März 2008 Schweitzer, J. & IPY Project Consortium (2008), The IPY Project “The Dynamic Continental Margin between the Mid-Atlantic-Ridge System (Mohns Ridge, Knipovich Ridge) and the Bear Island Region”. 39th Nordic Seismology Seminar, June 4-6, 2008, Oslo Sørensen, M.B., Voss, P., Havskov. J., Gregersen, S., and Atakan, K. 2008. Seismotectonics of Skagerrak. Nordic Seismology Seminar, Oslo, Norway, 4-6 June 2008.

7. References

Alsaker A., Kvamme, L.B., Hansen, R.A., Dahle, A. and Bungum, H. (1991): The ML scale in Norway. Bull. Seism. Soc. Am., Vol. 81, No. 2, pp.379-398.

Andersen K. (1987): Local seismicity and volcanism in the Jan Mayen area. McS., Department of geosciences, University of Bergen.

Atakan,K., Lindholm,C.D., and Havskov,J. 1994. Earthquake swarm in Steigen, northern Norway: An unusual example of intraplate seismicity. Terra Nova 6, 180-194.

Brune J.N. (1970): Tectonic stress and spectra of seismic shear waves. Journal of Geophysical Research, 75, 4997-5009.

Grünthal, G. (1998): "European Macroseismic Scale 1998". Cahiers du Centre Européen de Géodynamique et de Séismologie Volume 15, Luxembourg.

Havskov J., and Bungum, H. (1987): Source parameters for earthquakes in the northern North Sea. Norsk Geologisk Tidskrift,Vol.67, pp 51-58.

Havskov, J. and Ottemöller, L. (1999): SEISAN earthquake analysis software. Seism. Res. Letters, Vol. 70, pp. 532-534.

Havskov, J. and Ottemöller, L. (2001): SEISAN: The earthquake analysis software. Manual for SEISAN v. 8.0, Department of Earth Science, University of Bergen, Norway.

Havskov, J. and Sørensen, M.B. (2006): New coda magnitude scales for mainland Norway and the Jan mayen region. NNSN Technical report no. 19.

Kanamori, H. (1977): The energy release in great earthquakes. Journal of Geophysicsl Research 82; 20, pp. 2981-2987.

Karnik, V., Kondorskaya, N.V., Riznichenko, Y. V., Savarensky, Y. F., Solovev, S.L., Shebalin, N.V., Vanek, J. and Zatopek, A. (1962): Standardisation of the earthquake magnitude scales. Studia Geophys. et Geod., Vol. 6, pp. 41-48.

Kennett, B.L.N. and Engdahl, E.R. (1991): Traveltimes for global earthquake location and phase identification. Geophys. J. Int., Vol. 105, pp. 429-465.

Kradolfer, U. (1996): AuroDRM – The First Five Years. Seismological Research Letters, vol. 67, no. 4, 30-33.

Lienert, B.R. and Havskov, J. (1995): HYPOCENTER 3.2 A computer program for locating earthquakes locally, regionally and globally. Seismological Research Letters, Vol. 66, 26-36.

Moreno, B, Ottemöller, L., Havskov, J. and Olesen, K.A. (2002): Seisweb: A Client-Server- Architecture-Based Interactive Processing Tool for Earthquake Analysis. Seism. Res. Letters. Vol.73, No.1.

Ottemöller, L. (1995): Explosion filtering for Scandinavia. Technical Report No. 2, Institute of Solid Earth Physics, University of Bergen, Norway.

Sørensen, M.B., Ottemöller, L., Havskov, J., and Atakan, K., Hellevang, B., Pedersen, R.B. 2007. Tectonic processes in the Jan Mayen Fracture Zone based on earthquake occurrence and bathymetry. Bulletin of the Seismological Society of America, Vol.97 No.3, 772-779, doi: 10.1785/0120060025. Veith K.F., and Clawson, G.E. (1972): Magnitude from short-period P-wave data. Bull. Seism. Soc. Am., Vol. 62, pp.435-452.

Westre S. (1975): Richter's lokale magnitude og total signal varighet for lokale jordskjelv på Jan Mayen. Cand. real thesis., Seismological Observatory, University of Bergen, Norway.

The NORSAR Station and Arrays

NORSAR currently operates three seismic arrays (ARCES in Finnmark (25 sites), SPITS on Spitsbergen (9 sites) and NOA in southern Norway (42 sites)) and the broadband station JMIC on Jan Mayen. The fourth seismic array NORES (25 sites) was hit by lightning in 2002 and is under reconstruction. Additionally NORSAR collects data from the FINES array in southern Finland and the HFS array in southern Sweden. The data streams are available in realtime at NORSAR and are subjected to immediate automatic processing and analyses. All waveform and parametric data are openly available and can be accessed through web- interfaces or direct means.

Fig. 1. NORSAR seismic station JMIC and arrays NOA, ARCES, SPITS (and NORES under reconstruction).

The NORSAR webpage www.norsardata.no provides access to general station information, to automatic and reviewed seismic bulletins, to real-time plots of short and long-period data and to an AutoDRM request form for waveform data retrieval.

1 Systems Recording Performance

The arrays have continuous data recording. In 2008 the data completeness for the SPITS array was 89.41%, for the ARCES array 98.55%, and for the NORSAR array 97.81%. The performance in terms of monthly completeness statistics is shown in Table 1.

ARCES SPITS NORSAR

January 99.639% 99.639% 98.408% February 99.913% 99.913% 97.130% March 99.449% 99.449% 95.235% April 98.588% 98.588% 95.236% May 93.276% 93.276% 95.234% June 95.062% 95.062% 95.766% July 99.831% 71.400% 95.418% August 97.222% 60.063% 87.081% September 99.782% 59.671% 96.234% October 100% 99.994% 97.238% November 99.968% 100% 97.939% December 99.859% 95.908% 99.004% Table 1. Systems recording performance (in % of data completeness) for three arrays operated by NORSAR in 2008.

2 Detections

The NORSAR analysis results are based on automatic phase detection and automatic phase associations which produce the automatic bulletin. Based on the automatic bulletin a manual analysis of the data is done, resulting in the reviewed bulletin. The automatic bulletin for northern Europe is created using the Generalized Beam Forming (GBF) method. This bulletin (www.norsardata.no/NDC/bulletins/gbf/) is subsequently screened for local and regional events of interest in Fennoscadia and in Norway, which in turn are reviewed by an analyst. Regional reviewed bulletins from NORSAR are available from 1989 and from 1998 onwards they are directly accessible from via internet (www.norsardata.no/NDC/bulletins/regional/). Table 2 gives a summary of the phase detections and events declared by GBF and the analyst.

Jan. Feb. March April May June

Phase detections 154415 145482 161045 141179 156807 141294 Associated phases 4564 9622 7540 6329 6086 5103 Un-associated phases 149851 135860 153505 134850 150721 136191 Screened GBF events for 941 1719 1456 1158 1155 1000 Fennoscandia/Norway No. of events defined by 51 182 81 94 94 75 the analyst July Aug. Sep. October Nov. Dec. Phase detections 171338 181645 138281 195823 159442 173256 Associated phases 6042 7087 5645 8332 5597 5864 Un-associated phases 165296 174558 132636 187491 153845 167392 Screened GBF events for 1198 1589 1178 1713 1205 1345 Fennoscandia/Norway No. of events defined by 78 76 87 96 83 52 the analyst Table 2. Phase detections and event summary.

3 Combined NORSAR-UiB data analyses

Array processing is fundamentally different to single-station processing and there is no straightforward way to merge and commonly process array and single-station waveform data. However, on a higher level parameters like phase arrival readings from array beams and single stations can be combined and be used for event localization. At NORSAR the parameters of analyst-reviewed events are converted into parameter files in Nordic format and forwarded via ftp to UiB on a daily basis. The magnitude threshold has been lowered to about M 1.5 for regional events of potential interest for the NNSN. After transferring the parameter files, the NORSAR analyst logs into the the UiB data base using SEISAN and integrates the events. Integration means to merge NORSAR and UiB events, which may require to repick seismic phases, to include new phase readings, to edit double phase readings and to relocate the seismic event with the new parameters.

4 NORSAR-UiB data streams

All historic and realtime NORSAR data can be downloaded using the well-known automated Data Request Manager (AutoDRM). In addition NORSAR has established a seedlink server (athene.norsar.no) that provides realtime data streams from all NORSAR broadband instruments. UiB is currently receiving 10 three-components streams from stations AREO, JMIC, NAO01, NB201 NBO00 NC204, NC303, NC405, NC602, SPA0, which can be integrated into their single-station processing schemes.