Appendix G

Documentation of the Swiss instrumental earthquake catalog, 1975-2008. Nicholas Deichmann and Souad Sellami, SED, 2009/12/23 1. Station networks 1.1 National high-gain network 1975 – January 2002: Short-period, FM telemetry. Mainly vertical component 1-second MARK L4 and 2-second Wilmore sensors; some stations with 3 components and some stations with an additional vertical-component low-gain channel. Documented in Mayer-Rosa et al (1983), Deichmann et al. (2000), SED Annual Reports 1996-2001. September 1998 - present: Broad-band, digital data transmission. All three-component, mostly STS-2 sensors, some Lennartz 5-second sensors and a few Lennartz 1-second sensors. Documented in the SED Annual Reports 1998-2008. 1.2 Tseuzier network: Fall 1981 - August. 1989: six-station network in the vicinity of the Tseuzier hydroelectric reservoir (Wallis) to monitor the local seismicity. Vertical MARK L4 1-second sensors; analog telemetry recorded on site. September 1989 - August1992: Three of the single component stations (ZZB, ZZC and ZZD) were replaced by a three-component MARK L4 connected directly to the data recorder (Station ZZG, higher dynamic range). The three remaining single-component stations (ZZA, ZZE and ZZF) were decommissioned in December 1991. Documented in Perraudin (1981), Maurer (1993), Deichmann et al. (2000).

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1.3 Nagra network in northwestern Switzerland July 1983 – November 1983: Three single stations (ACB, CHE1 and GIF1) with three-component 1 sec MARK L4 seismometers, recording on site on FM-magnetic tape. November 1983 – August 2001: Six vertical component MARK L4 1-second sensors (stations EIT, ENB, GEF and GIF) and two three-component MARK L4 1-second sensors (stations ACB and CHE). The signals of five stations were transmitted by analog FM telemetry to the recording site at Cheisacher; the three channels of station CHE were recorded on site (higher dynamic range). As of May 1997 station EIT was closed. As of end of August 2000, stations TSB and ENB were closed and the data of the remaining stations were transmitted directly to SED; In September 2000, station CHE was renamed to SULZ and its short-period sensor was replaced by an STS2 broad-band sensor. Stations RBF and GEF were closed July and August 2001. June 1984 – May 1999: One additional station (IRC, analog FM telemetry, 1-second vertical MARK-L4 sensor) was recorded at SED; at first on a separate data acquisition system, together with stations SLE, ZLA and WIL of the national network, later integrated directly in the national network. Documented in Mayer-Rosa et al. (2004), Deichmann et al. (2000), SED Annual Reports 1996 – 2001. 1.4 Kaiseraugst temporary network November 1986 - October 1989: Single stations, analog magnetic tape recording on site, single- and three-component 1-second MARK L4 sensors. Documented in Kaiseraugst Technical Reports (unpublished) and in Deichmann (1990). 1.5 NFP-20 temporary network in Graubünden November 1986 - September 1988: Nine single stations, analog magnetic tape recording on site, single-component 1-second MARK L4 sensors. Documented in Roth (1990).

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1.6 Nagra network in central Switzerland November 1988 – March 1998: Three single stations, analog magnetic tape recording on site, single- and three-component 1-second MARK L4 sensors. Documented in Deichmann et al. (2000) and in SED Annual Reports 1996 – 1998. 1.7 NFP-20 temporary network in the Valais August 1989 - October 1991: Eleven single stations, analog magnetic tape recording on site, single-component 1-second MARK L4 sensors. Documented in Maurer (1993). 1.8 Nagra network northeastern Switzerland September 2003 – present: Three-component, 5-second Lennartz sensors, digital data transmission, data integrated in national broad-band network in real-time. Documented in internal report to Nagra and in SED Annual Reports 2003-2008. 1.9 AlpTransit network Gotthard October 2005 – present: Local network installed to monitor the induced seismicity in conjunction with the construction of the new Gotthard railway tunnel. It consists of eight stations with three-component 1-second Lennartz sensors and two strong-motion instruments. An additional broad-band station was added in January 2008 (PIORA). Documented in internal reports to AlpTransit AG and in SED Annual Reports 2005 – 2008. 1.10 Basel Deep-Heat-Mining borehole network November 2006 - present Six three-component short-period borehole sensors at depths between 300 and 2700 meters to monitor the seismicity induced by the geothermal project in Basel (operated by Geothermal Explorers Ltd.). Documented in internal report to Geopower Basel AG and in SED Annual Report 2006.

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1.11 Strong-motion networks November 1991 – present: Low-dynamic range instruments (12-16 bit) installed at about 50 free-field sites and as part of five mini-arrays in the dams of some of the largest hydropower reservoirs (Emosson, Mauvoisin, Grande Dixence, Mattmark and Punt dal Gall). The data is accessed by dial-up for significant events and at present has been only partially integrated into the SED waveform archive. 2003 – present: High-dynamic range instruments (24 bit) at presently 12 sites of the high-gain broad-band network with continuous real-time data transmission to SED. 2006 – present: High-dynamic range instruments (24 bit) at presently 20 sites (partly replacing instruments of the old low-gain network and partly at new sites) with continuous real-time data transmission to SED. An additional six online strong-motion instruments are part of the AlpTransit Gotthard network. Since 2006, the data from these strong-motion instruments are being used routinely also for computing earthquake locations. 1.12 Foreign networks Arrival-time data from foreign networks (in particular data from the seismic networks operated by the University of Karlsruhe, the Landeserdbebendienst Baden-Württemberg, the University of Genova and the University of Grenoble) have already been used for source locations and focal mechanisms as far back as 1983; however, this was only done for some significant events. Initially, waveforms from foreign networks have also been integrated sporadically and manually into the SED waveform archive during re-analysis long after the events had occurred. In 2000, an automatic procedure was implemented to automatically collect additional waveforms via AUTODRM from some foreign stations within a few minutes after an initial automatic location if they might improve the azimuthal station coverage. Then beginning in 2005, data from stations in a more or less extended border region operated by Austrian, Italian and German networks have been integrated in real-time into the continuous data stream of the SED and are now used routinely for computing earthquake locations. 2. Data acquisition systems 2.1 National high-gain network: 1974 – 1986: Continuous analog recording on microfilm; some prominent events were also recorded and archived on PCM tapes and later digitized, but are not integrated in the present digital waveform archive. The detected events on the microfilms were subsequently scanned and archived as digital images (gif).

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September 1983 - September 1992: Analog telemetry signals transmitted to a central digital recording site with event detection on a10-bit digitizer with 64 Hz sampling rate, (HP-F1000 computer, named FHP). November 1991 - January 2002: Analog telemetry signals transmitted to a central digital recording site with event detection on a 12-bit digitizer with 64 Hz sampling rate (HP-A800 computer, named AHP). (Due to the non-linearity of the FM telemetry system, the amplitudes of the short-period digital records start to become unreliable at about 60% of the digital clipping level!) September 1998 – present: Digital broad-band data recorded on site by a 24 bit data logger and transmitted in packets in real-time to the SED. Nominally the sampling rate of the high-gain broad-band network is 120 Hz and of the online strong-motion network it is 250 Hz. 2.2 Tseuzier and Nagra northern Switzerland: Analog telemetry signals digitized (100Hz sampling rate) and recorded on a Kinemetrics PDR-2 data logger. Except for stations CHE and ZZG, the bandwidth and dynamic range are limited by the FM telemetry system. Stations CHE and ZZG were recorded at the site of the PDR-2 with automatic gain ranging; their dynamic range and amplitude reliability is considerably higher. As of September 1994, the PDR-2 data loggers at station CHE were replaced by a PC-based data acquisition system (12-bit digitizer) with the IASPEI digital data acquisition software developed by Willy Lee of the USGS. The signals of station CHE were recorded at two different gain levels and then combined to a single "gain-ranging channel" during post-processing. Documented in Deichmann et al (2000). 2.3 Kaiseraugst, NFP-20 Graubünden/Wallis and Nagra central Switzerland: The data of these four temporary networks were recorded continuously on site by a very slow-moving analog tape recorder. The tapes were then played back at a much higher speed, and seismic events were extracted with an event detector. Most of the installations consisted of a single vertical component seismometer, whose signals were recorded on three different channels with different gains, to offset the very restricted dynamic range of the recording system. In a few cases the three channels were used instead to record the signals of a three-component sensor. A fourth channel was used for time synchronization to record a radio-transmitted time signal (DCF). At first, the analog signals were displayed on a paper chart. The arrival times and amplitudes were measured from these charts with a ruler. Later, all the recorded seismic events were digitized and integrated into the seismic event waveform archive of the SED. Documented in the Appendix of Maurer (1993).

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3. Data processing and archiving 3.1 Arrival times and amplitudes 1974 – 1986: Arrival times and amplitudes were read with a ruler from microfilm recordings projected onto a light-table with a time scale of 2 mm/s. September 1983 – 1992: Digital data was plotted on paper (routinely at 2 mm/s and for significant events at 10 mm/s); arrival times and amplitudes were measured manually on a digitizing tablet. 1992 – present: Interactive arrival-time and amplitude measurements on a computer screen with the SNAP software developed at SED (M. Baer). This software has also been used for a later re-analysis of several events dating back as far as November 1983. 3.2 Location programs 1975 – 1999: hypo-71, based on a 1D velocity model with variable Moho depth. 1998 – present: grid_search, based on a 1D velocity model with variable Moho depth. 2005 – present: nonlinloc, based on a 3D velocity model 3.3 Waveform data archives 1974 – 1986: Develocorder films in the archive of the ETH library. November 1974 - December 1986: Event scans (.gif) of the Develocorder signals on 6 CDs (two copies in SED safe). Digitized PCM event data (4 Dat-Tapes in SED safe). September 1983 – present: Digital event waveform files in GSE2 format stored as /events/yyyy/mm/KPyyyymmddhhnn.GSE2 This waveform archive is essentially complete from 1995 to the present (every event in the catalog has a corresponding waveform file), but completeness decreases going back in time beginning in 1994.

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4. Catalog status In this section we give an overview of the present status of the Swiss instrumental catalog and of the available documentation. The instrumental earthquake parameter archive of the SED consists essentially of three ASCII text files per event stored as /events/yyyy/mm/KPyyyymmddhhnn.* Here the * stands for one of three file name extensions: MANUPICK: the manually revised arrival times and maximum amplitudes for each station; MANULOC: a one-line file with the condensed location results; MANUPDE: the complete output of the location software. These files are stored in the same directory as the event waveform files. Quarry blasts and other explosions (seismic refraction shots, construction blasts and a military accident) are flagged with an “E” in the MANULOC-files. Events that are neither earthquakes nor explosions (such as landslides and avalanches) are stored in a directory of their own (/events/varia/). In the course of the catalog revision, efforts were made to check and ensure consistency among these three files and the corresponding waveforms. The complete location results (MANUPDE-files) have only been archived routinely since about 2001. Before that year, these files exist only for events that have been re-analyzed recently. The GSE2 waveform files are essentially complete from the year 1995 onward. Before that time, the data were either acquired only in analog form (Develocorder) or the missing digital waveform files have been deleted. For the purpose of this Appendix, we subdivide the instrumental catalog into three periods: 1975 – 1983, 1984 – 1995 and 1996 – 2008. The end of 1983 marks the start of the transition from analog to digital data and therefore corresponds to a significant milestone in the evolution of the instrumental catalog. From the standpoint of the type of waveform data, the end of the short-period network at the beginning of 2002 would be the next significant milestone. However, in 1996 the SED has revived the long-standing tradition of publishing an annual report of the earthquake activity in Switzerland and surroundings. So 1996 marks a significant milestone in the documentation of the earthquake catalog. In the following, because it is more expedient to discuss the earlier periods in light of the present status of the data base behind the catalog, we comment on these three periods in reverse order. 4.1 1996 – 2008 Since 1996, annual reports summarizing the seismic activity in Switzerland and surrounding regions have been published in the second or third issue of the Eclogae Geologicae Helvetiae - Swiss J. Geosciences of the following year. In a slightly different form and in some instances with updated information that was not available at the time of publication, these annual reports are also accessible via internet from http://histserver.ethz.ch/seismotectonics/reports.php. These reports include a list of all events with local magnitudes of at least 2.5, faultplane solutions and moment tensors of the most significant events, macroseismic intensity maps of felt events, a documentation of unusual earthquake sequences and of other significant non-earthquake and non-explosion events such as landslides, avalanches or accidents that left seismic traces over the past year.

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Figure 1: Epicenter map of all earthquakes (5574 events) with ML > 0 in the SED data archive for the years 1996 – 2008. In preparing the annual report the data is reviewed according to the following procedure:

1. we search for unidentified quarry blasts, by comparing the locations of events that occurred during daylight and weekdays with known quarry locations, and by checking the recorded signals for typical signs of a near-surface explosive source;

2. we review all locations with an rms > 0.5; 3. we review all events with focal depths > 15 km; 4. we review all events with Ml > 2.4.

This procedure has resulted in a high degree of internal consistency of the catalog for this time period. In addition, as of October 2003 routine data analysis has been restricted to only two and as of March 2007 to three experienced seismologists. Earlier on, a group of about a dozen persons with variable degrees of experience and motivation took turns doing the routine data analysis. Nevertheless, in some cases discrepancies remain between the contents of the SED data archive and the information in the updated annual reports as posted on the SED website. This is due to the fact that hypocentral locations published in the annual reports can be based on additional information, such as 2D ray-tracing or data that for technical reasons could not be integrated in the data structure available for routine analysis. Were such discrepancies exist, the

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information in ECOS-09 has been manually modified to match the current status of annual reports as posted on the SED website. In Table 1, below, these events are labeled with a (c) and the location quality (Q) is not determined alone by the listed values of azimuthal gap (GAP) and minimum epicentral distance (DM), as explained in section 4.3, but reflects the fact that the location, and in particular the focal depth, are constrained by additional information. Date Time Lat Lon Z ML RMS GAP DM NO Q Location ----------------------------------------------------------------------------- 1996 03 31 06 08 01.1 45.938 7.460 4 4.2 0.05 220 18 9 A (I) Valpelline (c) 1996 05 17 09 30 59.4 47.170 9.488 1 3.6 0.37 188 14 19 B (SG) Buchs 1996 06 15 21 40 09.8 47.118 10.019 10 3.6 0.34 227 35 23 C (A) Arlberg 1996 06 28 09 57 48.5 47.118 10.012 10 4.1 0.30 226 35 31 C (A) Arlberg 1996 07 15 00 13 30.4 45.935 6.092 3 5.1 0.39 286 64 15 A (F) Annecy (c) 1996 07 23 04 08 41.6 45.947 6.071 2 3.9 0.32 288 65 24 A (F) Annecy (c) 1996 08 24 02 38 22.4 47.423 9.045 29 3.9 0.12 178 10 20 A (SG) Kirchberg 1997 04 12 23 00 00.0 46.511 10.438 10 3.5 0.12 295 30 12 D (I) Bormio 1997 11 22 04 56 10.6 47.134 9.189 1 3.8 0.28 92 17 19 A (SG) Walensee (c) 1998 04 21 02 30 56.0 47.143 9.344 10 3.6 0.24 130 12 26 A (SG) Walenstadt (c) 1998 12 09 22 08 14.3 46.191 7.552 4 3.4 0.09 107 16 10 A (VS) Grimentz (c) 1999 02 14 05 57 53.6 46.793 7.215 2 4.3 0.26 98 21 7 A (FR) Fribourg (c) 1999 05 14 18 25 28.8 46.737 8.000 6 3.9 0.21 65 10 24 B (BE) Brienz 1999 05 20 13 11 35.2 46.653 7.296 7 3.8 0.15 59 29 14 A (FR) Jaun 1999 12 29 20 42 34.8 46.550 10.304 5 4.9 0.09 186 10 6 B (I) Bormio (c) 1999 12 31 04 55 53.9 46.554 10.335 5 4.3 0.06 209 9 10 B (I) Bormio (c) 2000 02 23 04 07 07.2 47.046 9.501 7 3.6 0.22 104 9 10 A (SG) Bad Ragaz 2000 03 04 15 43 19.8 47.227 9.474 3 3.6 0.24 73 7 10 B (SG) Buchs 2000 04 06 17 40 36.7 46.533 10.359 5 4.2 0.10 224 6 11 B (I) Bormio 2000 06 03 15 14 10.7 47.206 10.102 2 3.9 0.32 176 19 9 B (A) Lech 2000 06 09 05 06 06.2 46.527 10.355 5 3.5 0.17 208 6 10 B (I) Bormio (c) 2000 06 10 05 51 02.1 47.206 10.104 3 3.6 0.14 177 19 10 B (A) Lech 2001 02 23 22 19 41.7 46.136 7.031 6 3.6 0.17 94 6 17 A (VS) Martigny 2001 02 25 01 22 30.9 46.133 7.028 7 3.5 0.17 99 6 17 A (VS) Martigny 2001 03 17 00 29 59.8 46.920 9.006 3 3.8 0.22 80 8 21 A (GL) Linthal 2001 04 06 02 22 52.6 45.870 9.234 22 3.8 0.25 210 38 20 C (I) Erba 2001 10 01 06 36 22.2 46.553 10.335 5 4.2 0.20 202 9 12 B (I) Bormio (c) 2002 04 29 15 14 09.3 46.102 8.457 21 3.8 0.28 120 36 9 B (I) S.Maria Maggiore 2002 05 31 16 50 33.4 46.321 7.359 5 3.5 0.14 114 6 14 B (VS) Anzere 2003 04 29 04 55 09.1 46.341 7.570 10 3.9 0.20 90 6 32 A (VS) Salgesch 2003 05 06 21 59 43.4 46.905 8.908 3 4.0 0.18 72 8 17 A (UR) Urnerboden 2003 07 17 02 27 16.1 46.729 9.838 7 3.6 0.16 88 7 13 A (GR) Sertig 2003 07 18 11 01 35.8 46.723 9.840 7 3.9 0.18 84 7 14 A (GR) Sertig 2003 08 01 03 20 23.4 46.729 9.837 7 3.9 0.13 81 7 17 A (GR) Sertig 2003 08 22 09 21 32.2 46.323 7.316 6 3.9 0.25 70 5 28 A (VS) Glarey 2003 08 22 09 30 09.4 46.318 7.315 6 3.6 0.26 71 5 24 A (VS) Glarey 2004 02 23 17 31 21.0 47.278 6.270 15 4.8 0.12 166 41 10 B (F) Besancon 2004 06 21 23 10 02.2 47.505 7.713 22 3.8 0.16 82 5 40 A (BL) Liestal 2004 06 28 23 42 30.1 47.525 8.169 20 4.0 0.13 75 4 50 A (AG) Brugg 2005 05 12 01 38 05.6 47.265 7.655 25 4.1 0.11 79 9 23 A (BE) Rumisberg 2005 09 08 11 27 17.6 46.037 6.889 4 4.9 0.21 81 4 24 A (F) Vallorcine (c) 2005 11 12 19 31 16.3 47.521 8.166 20 4.1 0.12 75 4 37 A (AG) Brugg 2006 04 12 22 24 53.2 46.597 10.255 2 3.5 0.09 208 3 8 A (GR) Val Mora 2006 10 20 00 11 58.2 45.721 10.332 2 3.6 0.37 150 19 9 B (I) Valli Giudicarie 2007 03 23 05 01 38.4 45.690 9.867 10 3.6 0.40 99 15 21 B (I) Bergamo 2007 05 19 16 19 38.6 47.168 10.605 2 3.9 0.29 79 36 19 C (A) Landeck 2008 01 21 16 40 35.5 46.759 9.447 8 4.0 0.26 56 9 75 A (GR) Paspels (c) 2008 02 17 12 41 31.3 45.920 7.171 7 3.6 0.31 100 19 48 B (VS) Lac des Toules 2008 11 09 07 22 31.3 46.793 9.204 8 3.7 0.29 30 16 77 A (GR) Ilanz (c)

Table 1: Earthquakes in Switzerland and surroundings during the period 1996 - 2008 with ML >= 3.5.

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Figure 2: Epicenter map of all events identified as explosions (1035 events) in the SED data archive for the years 1996 – 2008. These explosions comprise quarry blasts as well as construction blasts and seismic refraction and reflection shots (some of the latter were set off in the middle of the night). It is clear that even the most careful data analysis can not guarantee that all quarry blasts have been identified and that no earthquakes have been erroneously classified as explosions. Figure 3 shows histograms of the number of events identified as earthquakes as a function of the time of day for all events and only for events with ML >= 2.0. The lack of a higher activity during day-time indicates that whatever the number of unidentified explosions might be, during this time period, it is in no way statistically significant. The larger number of events at night in the plot of all events reflects the increased sensitivity of the network due to the generally lower man-made noise level during night-time. This effect disappears for larger magnitudes.

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Figure 3: Histograms of the number of earthquakes as a function of the time of day (local time adjusted for daylight-saving time) during 1996-2008, for all events (left) and only for events with ML >= 2.0 (right). A procedural change during this period with important consequences for the catalog occurred on August 27th 2001, when the event detection system was switched from the short-period to the broad-band network. Because of the higher upper limit of the instrument frequency bandwidth (40 Hz instead of 12.5 Hz) the event detection became more sensitive to small high-frequency events. This resulted in a sharp increase in the cumulative number of recorded events and will probably have an effect on the magnitude of completeness after that date. 4.2 1984 – 1995 This is a time period characterized by the operation of several temporary networks (Tseuzier, Nagra central Switzerland, Kaiseraugst and NFP-20 seismotectonic studies in Graubünden and the Wallis. The event locations for this period have been reviewed according to the procedure described above only for the year 1995. Thus, except for some particular events that were re-analyzed later to construct a focal mechanism or to correct some mistake that were recognized during the magnitude analyses discussed in Appendix H and K, the data base for this period essentially corresponds to the results of the routine analysis performed at the time of the event. However, a systematic search for undetected explosions, based on time of occurrence, location in the proximity of known quarries and waveform characteristics has been undertaken for this revision of the catalog also for this period. The histograms of the number of earthquakes as a function of time-of-day in Figure 6 show a slight increase in the seismic activity during the afternoon. This could be an indication that the catalog still includes some explosions erroneously identified as earthquakes.

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Figure 4: Epicenter map of all earthquakes (3045 events) with ML > 0 in the SED data archive for the years 1984 – 1995. In the original data archive of the SED, about 500 events between 1984 and 1991 have a magnitude of 0 or less and have not been included in ECOS-09. These events are either recorded only by the local network around the hydropower dam of Tseuzier or by one of the NFP-20 networks in Graubünden or the Wallis, for which magnitudes were not computed. In Table 2, below, we list all events with ML >= 3.5 in Switzerland and surroundings during this time period. Locations of events labeled with (c) have been modified with respect to the information in the data archive of the SED based on more detailed analyses published in the literature. For the Mauvoisin, Zermatt and Mont Blanc events see Eva et al. (1998); for the Fribourg quakes of 1987 and 1995 see Kastrup et al. (2007); a detailed analysis of the earthquake of Vaz and its aftershocks can be found in Marone (1999); the location of the Wutöschingen event is from Bonjer (1997) and of the Grand Bornand event from Frechet et al. (1994).

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Date Time Lat Lon Z ML RMS GAP DM NO Q Location ----------------------------------------------------------------------------- 1984 06 08 02 43 34.9 46.688 10.323 10 4.0 0.18 289 14 12 C (GR) S-Charl 1984 09 05 05 16 49.3 47.247 8.562 15 4.0 0.10 95 18 26 A (ZH) Albis 1985 01 04 16 57 37.0 46.002 7.269 10 3.5 0.07 202 14 8 A (VS) Mauvoisin (c) 1985 05 21 17 43 27.4 46.680 10.628 3 3.6 0.41 304 38 25 D (I) Val Venosta 1986 01 28 11 49 48.1 46.434 7.877 12 3.5 0.11 127 31 18 B (VS) Loetschental 1986 02 15 01 43 06.6 46.061 7.638 5 3.8 0.19 176 18 19 A (VS) Zermatt (c) 1986 02 27 12 07 06.7 47.684 8.958 18 4.1 0.11 153 27 11 A (TG) Steckborn 1987 09 20 11 53 57.8 46.758 7.215 2 3.9 0.13 105 19 18 A (FR) Fribourg (c) 1987 10 28 23 49 00.4 47.076 9.206 13 4.2 0.31 51 22 55 A (GL) Muertschenstock 1987 11 05 22 06 58.8 46.413 8.104 13 3.5 0.09 96 39 22 B (VS) Fiesch 1987 12 04 14 45 11.0 45.838 10.569 4 4.2 0.44 296 101 30 D (I) Valli Giudicarie 1987 12 11 02 25 58.2 47.314 7.163 9 3.7 0.14 61 26 36 B (JU) Glovelier 1988 06 11 22 44 45.1 45.861 6.886 8 3.7 0.05 313 25 12 A (F) Mont Blanc (c) 1989 01 07 02 29 41.5 46.345 7.534 6 3.6 0.04 63 6 13 A (VS) Montana 1989 09 30 04 41 02.1 46.328 7.388 8 4.1 0.14 113 4 20 A (VS) Wildhorn 1990 02 14 15 55 54.0 46.283 6.749 17 4.2 0.25 119 27 24 B (F) Bonneveaux 1990 03 18 09 54 30.7 46.791 9.834 3 3.5 0.14 108 8 25 A (GR) Davos 1990 05 16 12 32 27.0 46.858 10.237 15 4.0 0.46 255 20 31 C (GR) Piz Tasna 1990 11 22 15 51 19.3 46.893 9.004 5 3.7 0.27 62 5 65 A (GL) Linthal 1991 11 20 01 54 17.6 46.731 9.527 6 5.0 0.15 120 24 10 A (GR) Vaz (c) 1992 02 17 19 23 13.3 46.726 9.529 10 3.6 0.06 124 24 7 B (GR) Vaz 1992 03 28 19 24 16.2 46.741 9.512 9 3.5 0.10 132 24 7 B (GR) Vaz 1992 05 08 06 44 40.2 47.145 9.518 2 4.7 0.32 185 18 13 B (SG) Buchs 1992 05 08 07 51 25.4 47.144 9.519 1 4.0 0.38 185 18 15 B (SG) Buchs 1992 05 15 00 43 43.2 47.158 9.525 11 3.9 0.37 187 17 17 B (SG) Buchs 1992 12 30 21 34 12.1 47.710 8.380 22 4.0 0.05 183 11 15 A (D) Wutoeschingen (c) 1993 06 14 12 28 36.6 46.003 8.262 19 4.2 0.17 201 24 7 C (I) Domodossola 1993 07 10 08 59 09.0 47.140 10.114 10 4.1 0.36 249 41 12 C (A) Arlberg 1993 12 09 18 16 50.6 45.708 10.258 10 4.0 0.46 283 106 29 D (I) Val Trompia 1994 03 31 09 41 42.8 47.132 10.102 10 4.3 0.33 236 40 20 C (A) Arlberg 1994 08 28 06 04 45.3 46.871 8.772 4 3.9 0.34 61 12 15 A (UR) Schaechental 1994 12 14 08 55 59.4 45.958 6.425 10 4.5 0.25 264 38 10 A (F) Grand Bornand (c) 1995 05 24 20 45 37.2 46.594 6.388 10 3.6 0.16 176 11 15 A (VD) Montricher 1995 06 25 18 53 07.4 47.603 8.862 11 3.6 0.07 227 20 11 A (TG) Frauenfeld 1995 09 17 16 29 24.4 46.787 7.198 2 3.6 0.26 144 18 30 A (FR) Fribourg (c) 1995 10 07 01 37 31.2 46.797 7.208 2 3.5 0.19 130 19 38 A (FR) Fribourg (c) 1995 11 16 05 57 21.3 47.057 8.798 4 4.0 0.41 62 16 12 A (SZ) Iberg Table 2: Earthquakes in Switzerland and surroundings during the period 1984 - 1995 with ML >= 3.5.

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Figure 5: Epicenter map of all events identified as explosions (450 events) in the SED data archive for the years 1984 – 1996. These explosions comprise quarries as well as construction blasts and seismic refraction and reflection shots (some of the latter were set off in the middle of the night). The large event in the center of the map was caused by the accidental explosion of a cavern used as an ammunition depository (ML = 3.6).

Figure 6: Histograms of the number of earthquakes as a function of the time of day (local time adjusted for daylight-saving time) during 1984-1995, for all events (left) and only for events with ML >= 2.0 (right).

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4.3 1975 – 1983 Until September 1983, the period 1975 - 1983 must be regarded as the pre-digital era of the Swiss seismological data. Although seismograms of some events have been digitized, the effort required to reformat the data and to correctly identify the individual traces is so large that for the revision of the earthquake catalog during this period we essentially have to rely on the results of the original data analysis alone. Thus, we have followed the following procedure:

1. The data have been retrieved from the original database and the events included in the section of the Swiss national map (at the scale of 1:500'000) have been kept: Swiss km-coordinates 480-865 / 62-302; Geographic coordinates 5.9-10.9E / 45.7-47.9N.

2. A quality has been applied according to the following criteria (see the annual reports of the SED): A: (RMS < 0.4, GAP < 180, DM < 1.5*Z) errH < 2 km, errZ < 3 km. B: (RMS < 0.6, GAP < 200, DM < 25) errH < 5 km, errZ < 10 km. C: (GAP < 270, DM < 60) errH < 10 km, Z undetermined D: (GAP > 270 or DM > 60) errH > 10 km, Z undetermined GAP = largest azimuthal angle between epicentre and two neighbouring stations (deg.), DM = minimum epicentral distance (km), RMS = root-mean-square of the travel-time residuals (s), Z = focal depth (km), errH = estimated horizontal location error, errZ = estimated vertical location error.

3. The events for which more reliable locations are available in the literature (events outside

Switzerland and events which were studied in more detail) have been corrected. 4. The events with no magnitude or an rms larger than 1.5 have been removed.

5. The explosions identified by the original data analyst have been flagged.

6. A further cleaning of the catalog, to search for unidentified explosions has been made.

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Figure 7. Map of the catalog 1974-1983 showing the location quality of the events (A=1 to D=4)

Catalog revison: The events have been sorted according to their depth, magnitude, location and time of the day (hour). In the plot of the time of day of the occurrence of each event as a function of the cumulative number of events (figure 2a) it appears that most of the events occur between 6 and 16 o’clock, with peaks around 9, 10, 14 and 15 o’clock. If we remove these events with focal depth = 0, the distribution with the time of day becomes more regular (figure 2b), and if we look at the events with a magnitude bigger than 2 (figure 2c), there is no more influence of the time of day.

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75-83 probable explosions depth 0

0

4

8

12

16

20

24

0 50 100 150

cum. number

hour

(utc

)

Figure 8a. Time of day vs. cumulative number of events with depth = 0 km.

1975-1983

0

4

8

12

16

20

24

0 500 1000

cum. number

hour

(UTC

)

Figure 8b. Time of day vs. cumulative number of events with depth > 0 km.

1975-1983 Mw > 2

0

5

10

15

20

25

0 50 100 150 200 250 300 350 400 450

cum. number

Figure 8c. Time of day vs. cumulative number of events, with Mw>2.

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We have made several plots to visualize and check the location of explosions. Figure 3 shows the events with a focal depth larger than 1, displayed on the location of known quarries. There potential explosions remain southwest of the Bodensee, in the French Jura and in the Rhone Valley between Martigny and Lac Léman. The last two sites consist of small events (magnitudes less than 2.1).

Figure 9. Map of the catalog 1974-1983 with a color scale indicating the time the day; underneath, in gray, are the locations of the identified quarries (or explosions) 1975-2008.

Many of the events with focal depth = 0 had already been identified as explosions by the original data analyst and their computed locations are in close proximity to known quarries. However, from the analysis of their location and time of day of their occurrence, it became clear that not all explosions had been identified by the analyst, and that a focal depth > 0 was

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not a sufficient criterion to identify the event as an earthquake. Thus a further systematic analysis of events suspected to be explosions based on their location in proximity of known quarries and the time of day of their occurrence led us to flag 52 additional events as explosions. The epicenter map with all those events that have been classified as explosions is shown in Figure 10 and as earthquakes in Figure 11. Despite additional efforts to identify previously unrecognized explosions, the histogram of all earthquakes as a function of the time-of-day still shows an increase in the seismic activity during afternoon hours. However, this increase is restricted to event magnitudes below ML = 2, as shown in the right-hand diagram in Figure 12. Thus, considering that the magnitude of completeness for this period most likely is not below ML = 2, these unrecognized quarry blasts will not be statistically significant.

Figure 10: Epicenter map of all events identified as explosions (205 events) in the SED data archive for the years 1975 – 1983.

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Figure 11: Epicenter map of all earthquakes (1640 events) with ML > 0 and with rms < 1.5 seconds in the SED data archive for the years 1975 – 1983.

Figure 12: Histograms of the number of earthquakes as a function of the time of day (local time adjusted for daylight-saving time) during 1975-1983, for all events (left) and only for events with ML >= 2.0 (right).

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In Table 3, below, we list all events with ML >= 3.5 located by SED in Switzerland and surroundings during the time period 1975 – 1983. Date Time Lat Lon Z ML RMS GAP DM NO Q Location ----------------------------------------------------------------------------- 1975 11 25 06 17 35.0 46.211 7.482 10 3.6 0.59 177 45 17 C (VS) Nax 1976 03 02 08 27 57.3 47.568 9.435 13 3.5 0.21 129 27 17 B (TG) Romanshorn 1976 03 26 22 28 31.3 47.576 9.443 5 3.7 0.26 171 85 20 B (TG) Romanshorn 1976 07 17 09 13 34.5 46.682 9.690 9 4.2 0.20 204 100 11 B (GR) Filisur (c) 1977 03 05 13 31 22.5 46.418 7.390 10 4.1 0.52 139 10 19 A (BE) Iffigenalp (c) 1977 03 10 02 01 42.4 45.891 10.113 10 3.5 0.22 312 105 7 D (I) Lovere 1978 01 16 21 05 42.8 45.813 8.753 1 3.5 0.23 250 108 5 D (I) Varese 1978 02 23 09 49 20.4 46.438 9.815 20 3.7 0.53 255 47 12 C (GR) Silvaplana 1979 07 03 21 13 10.9 46.922 7.063 30 3.8 0.32 186 22 10 B (FR) Murten (c) 1980 01 25 00 27 55.1 46.502 10.487 5 3.7 0.43 325 63 16 D (I) Bormio 1980 07 15 12 17 22.0 47.628 7.518 15 4.4 0.30 229 18 17 B (F) Sierentz 1980 07 15 12 54 46.0 47.647 7.478 11 3.7 0.56 233 20 19 B (F) Sierentz 1980 07 16 15 00 48.5 47.653 7.503 17 4.0 0.28 232 21 18 B (F) Sierentz 1980 07 22 22 46 23.2 47.652 7.507 17 3.6 0.33 252 21 13 B (F) Sierentz 1983 01 03 17 03 06.3 45.879 9.437 30 3.7 0.97 260 50 18 B (I) Lecco 1983 07 31 20 52 56.0 46.687 10.520 1 4.3 0.48 295 55 26 D (I) Val Venosta 1983 08 31 00 18 27.8 46.712 10.360 3 4.0 0.56 290 17 27 D (GR) S-Charl

Table 3: Earthquakes in Switzerland and surroundings during the period 1975 - 1983 with ML >= 3.5. Below are some remarks concerning the events listed in Table 3, for which additional information is available in the literature:

• Romanshorn (1976/03/26): Pavoni (1984, 1987) gives a focal depth of 10 km; this has been confirmed by a reanalysis of Kastrup (2002).

• Filisur and Iffigenalp: see Mayer-Rosa and Pavoni (1977), Jimenez and Pavoni (1983),

Garcia-Fernandez and Mayer-Rosa (1986).

• Murten: see Pavoni (1984, 1987); the large focal depth is confirmed by Garcia-Fernandez and Mayer-Rosa (1986).

• Sierentz: these four events belong to an extended sequence that was analyzed in detail by

Bonjer (1992, 1997); according to this analysis, the epicenters are around 47.67/7.48 and the focal depths between 10 and 13 km.

• Lecco: although the location of this event is poorly constrained by the SED data alone, the

large focal depth is real; in fact Zonno and Kind (1984) obtain a focal depth of 27 km for this event below the Southern Alps, based on modeling signals recorded at regional distances with synthetic seismograms.

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4.4 Summary of the seismic activity in Switzerland and surroundings, 1975 – 2008

Figure 13: Cumulative number of events, event magnitudes (ML) and mean (crosses) as well as median magnitudes (circles) of the earthquakes with ML > 0, recorded by the SED in Switzerland and surroundings, 1975 – 2008.

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Figure 13 summarizes the contribution to ECOS-09 by the SED concerning the seismic activity in Switzerland and immediate surroundings. Obviously the data is quite heterogeneous with time and the magnitude of completeness will vary accordingly. The pronounced increase in the number of low-magnitude events between the Fall of 1983 and the Fall of 1992 is due entirely to the operation of the local seismic network around the hydroelectric dam of Tseuzier, and will thus have only a very local impact on the magnitude of completeness. However, a more significant change of the magnitude of completeness will need to be taken into account after 2002, when the national network changed from the short-period to the broad-band system and additional stations came into operation, in particular in the Wallis.

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References Bonjer, K.-P. (1992): Seismizität als Zugang zu räumlichen und zeitlichen Anomalien der Spannungen in der Lithosphäre. In: Spannung und Spannungsumwandlung in der Lithosphäre. Berichtsband 1990-1992, Sonderforschungsbereich 108, Universität Karlsruhe, 985-1031, 1992. Bonjer, K.-P. (1997): Seismicity pattern and style of seismic faulting at the eastern borderfault of the southern Rhine Graben. Tectonophysics, 275,41-69, 1997. Deichmann, N. (1990): Seismizität der Nordschweiz, 1987-1989, und Auswertung der Erdbebenserien von Günsberg, Läufelfingen und Zeglingen. Nagra Technischer Bericht, NTB 90-46, Nagra, Baden. Deichmann, N., Ballarin Dolfin, D., Kastrup, U. (2000): Seismizität der Nord- und Zentralschweiz. Nagra Technischer Bericht, NTB 00-05, Nagra, Wettingen. Eva, E., Pastore, S., Deichmann, N. (1998): Evidence for ongoing extensional deformation in the western Swiss Alps and thrust-faulting in the southwestern Alpine foreland. Journal of Geodynamics, 26, 1, 27-43, 1998. Frechet, J., Thouvenot, F., Jenatton, L., Hoang-Trong, P., Frogneux, M. (1994): Le seisme du Grand-Bornand (Haute-Savoie) du 14 decembre 1994: un coulissage dextre dans le socle subalpin. C.R. Acad. Sci. Paris, 323, IIa, 517-524, 1994. Garcia-Fernandez, M. & Mayer-Rosa, D. (1986): Improved hypocentral parameter determination using secondary regional phases. Rev. de Geophysica, 42, 175-184. Jimenez, M.-J., Pavoni, N. (1983): Focal mechanisms of recent earthquakes, 1976-1982, and seismotectonics in Switzerland. In: Proc. Sess. 12, IASPEI XVIII Assembly, Hamburg 1983, H. Stiller and A. Ritsema, eds., Veroeff. Zentralinst. Physik der Erde, Potsdam, 1984, 77-84, 1983. Kastrup, U.(2002): Seismotectonics and stress field variations in Switzerland. Ph.D. Thesis Nr. 14527, ETH-Zürich, 2002. Kastrup, U., Deichmann, N,, Fröhlich, A., Giardini, D. (2007): Evidence for an active fault below the northwestern Alpine foreland of Switzerland. Geophys. J. Int., 169, 1273-1288, 2007, DOI: 10.1111/j.1365-264X.2007.03413.x Maurer, H. (1993): Seismotectonics and upper crustal structure in the western Swiss Alps. PhD Dissertation, ETH-Zürich. Marone, F. (1999): Das Magnitude 5 Beben von Vaz (Graubünden) von 1991: Seismotektonik und Auswertung der Nachbeben. Diplomarbeit, Institut für Geophysik, ETH-Zürich, 1999.

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Mayer-Rosa, D., Pavoni, N. (1977): Fault plane solutions of earthquakes in Switzerland from 1971 to 1976. Publ. Inst. Geophys. Pol. Acad. Sc., A-5 (116), 321-326, 1977. Mayer-Rosa, D., Benz, H., Kradolfer, U., Renggli, K. (1983): Inventar der Erdbeben 1910-1982 und Karten der Magnitudenschwellen-Werte 1928-1982. Nagra technischer Bericht, NTB 83-08, Nagra, Baden. Mayer-Rosa, D., Dietiker, M., Deichmann, N., Renggli, K., Brändli, J., Studer, J., Rutishauser, G. (1984): Mikrobeben-Untersuchung Nordschweiz, Teil 1: Technische Unterlagen, Stationsnetz. Nagra Technischer Bericht, NTB 84-11, Nagra, Baden. Pavoni, N. (1984): Seismotektonik Nordschweiz. NTB 84-45, Nagra, Baden, 1984. Pavoni, N. (1987): Zur Seismotektonik der Nordschweiz. Eclogae geol. Helv., 80/2, 461-472, 1987. Perraudin, F. (1981): Untersuchung der Seismizität des Gebietes zwischen Rawilpass und Zeuzier. Diplomarbeit Institut für Geophysik, ETH Zürich. Roth, P. (1990): Aktuelle Seismizität und Seismotektonik in den östlichen schweizer Alpen. PhD Dissertation, ETH-Zürich. SED Annual Reports, 1996 – 2008: http://histserver.ethz.ch/seismotectonics/reports.php Zonno, G. and Kind, R., (1984). Depth determination of north Italian earthquakes using Graefenberg data. Bull. Seis. Soc. Am., 74, 5, 1645-1659.