**7. The BASE-project as example for historical analysis**

The old Bavarian earthquake catalogue lists four events from the 14th until the 17th century, the earliest one being the 1390 event in Bad Reichenhall. BASE adds 232 events from the 4th century until the 17th century, the oldest one being a (questionable) earthquake recorded in Memmingen in 369 AD. The past few centuries are of course much better represented in the data base than the older ones. The renaissance of natural sciences after the 1500s led to a more profound occupation with natural hazards. More people noted earthquakes and reported them. As a not surprising result we have more detailed information about quakes for the past few centuries than for the time before 1500. More than half of all events filed in the BASE-catalogue date back to the 18th and 19th centuries, whereas the 10th and 15th centuries are, astonishingly enough, only sparsely represented (see Kárník's remark above).

A more problematic part of the assessment was the inclusion of earthquakes mentioned only in maps of important publications (especially Sieberg, 1940, whose compilation is problematic enough – see also Fig. 4). Those maps are in general quite speculative and only in very few cases specific. But in order to get a complete picture of the seismic situation in Bavaria it was necessary to include events which were shown as relevant for Bavaria in these maps. This resulted in the inclusion of at least 232 different earthquakes (project BASE II).

Thus, in a first step all existing data about earthquakes felt in Bavaria needed to be collected. This step was limited to already published data in 27 crucial publications over the past two centuries (Perrey, 1844; Boegner, 1847; Volger, 1857; Credner, 1884; Gümbel, 1889; Langenbeck, 1892, Günther, 1897; Günther n.d.; Gümbel, 1898; Brunhuber, 1903; Reindl, 1903a, 1903b; Günther & Reindl, 1904; Reindl, 1905a, 1905b; Credner, 1907; Reindl, 1907; Heritsch, 1908; Messerschmitt, 1907; Gießberger, 1922; Sieberg, 1940; Sponheuer, 1952; Schmedes, 1979; Leydecker & Brüning, 1988; Wolf & Wolf, 1989; Bachmann & Schmedes, 1993; Schmedes et al., 1993). The data were filed in a specially designed data base (Fig. 5), which was modified from the one successfully used in the HANG-project about natural hazards in the Alps (Barnikel, 2004). A second, future step will be the inclusion of (validated) contributions made by citizens all over Bavaria who share an interest in earthquakes and have access to local publications or documents which may have been denied wider distribution in journals or other scientific publications and are, therefore, largely unknown.

Germany's standard earthquake catalogue was first published by Leydecker (1986) in the year 1986 (in parts based on the catalogue published by Grünthal, for example in 1988) and issued on behalf of the German Federal Institute for Geosciences and Natural Resources. It claimed full coverage for all quakes from intensity MSK-1964 IV (Sponheuer, 1965) upwards and listed about 1900 events with either their epicentres in Germany or with macroseismic

Fig. 5. BASE data bank, screenshot.

numerous archives all over the state of Bavaria would have proven too time-consuming and costly by far (cf. Coeur et al., 1998; Barnikel & Becht, 2004), a new way had to be found to gather as much relevant information as possible in a shorter period of time. Especially local archives, which have found to be among the most productive and important sources for documents describing hazardous natural events from the 1800s and older (cf. Barnikel & Becht, 2003) cannot be screened by natural scientists alone. Eventually, people with access to local documents, like librarians or historians, need to be encouraged to contribute to the

The old Bavarian earthquake catalogue lists four events from the 14th until the 17th century, the earliest one being the 1390 event in Bad Reichenhall. BASE adds 232 events from the 4th century until the 17th century, the oldest one being a (questionable) earthquake recorded in Memmingen in 369 AD. The past few centuries are of course much better represented in the data base than the older ones. The renaissance of natural sciences after the 1500s led to a more profound occupation with natural hazards. More people noted earthquakes and reported them. As a not surprising result we have more detailed information about quakes for the past few centuries than for the time before 1500. More than half of all events filed in the BASE-catalogue date back to the 18th and 19th centuries, whereas the 10th and 15th centuries are, astonishingly enough, only sparsely represented (see Kárník's remark above). A more problematic part of the assessment was the inclusion of earthquakes mentioned only in maps of important publications (especially Sieberg, 1940, whose compilation is problematic enough – see also Fig. 4). Those maps are in general quite speculative and only in very few cases specific. But in order to get a complete picture of the seismic situation in Bavaria it was necessary to include events which were shown as relevant for Bavaria in these maps. This resulted in the inclusion of at least 232 different earthquakes

Thus, in a first step all existing data about earthquakes felt in Bavaria needed to be collected. This step was limited to already published data in 27 crucial publications over the past two centuries (Perrey, 1844; Boegner, 1847; Volger, 1857; Credner, 1884; Gümbel, 1889; Langenbeck, 1892, Günther, 1897; Günther n.d.; Gümbel, 1898; Brunhuber, 1903; Reindl, 1903a, 1903b; Günther & Reindl, 1904; Reindl, 1905a, 1905b; Credner, 1907; Reindl, 1907; Heritsch, 1908; Messerschmitt, 1907; Gießberger, 1922; Sieberg, 1940; Sponheuer, 1952; Schmedes, 1979; Leydecker & Brüning, 1988; Wolf & Wolf, 1989; Bachmann & Schmedes, 1993; Schmedes et al., 1993). The data were filed in a specially designed data base (Fig. 5), which was modified from the one successfully used in the HANG-project about natural hazards in the Alps (Barnikel, 2004). A second, future step will be the inclusion of (validated) contributions made by citizens all over Bavaria who share an interest in earthquakes and have access to local publications or documents which may have been denied wider distribution in journals or other scientific publications and are, therefore,

Germany's standard earthquake catalogue was first published by Leydecker (1986) in the year 1986 (in parts based on the catalogue published by Grünthal, for example in 1988) and issued on behalf of the German Federal Institute for Geosciences and Natural Resources. It claimed full coverage for all quakes from intensity MSK-1964 IV (Sponheuer, 1965) upwards and listed about 1900 events with either their epicentres in Germany or with macroseismic

growing data base as a kind of open-source catalogue.

(project BASE II).

largely unknown.

**7. The BASE-project as example for historical analysis** 

effects on Germany, but originating in neighbouring countries. Today it lists more than 2500 events relevant for Germany before 1906. Leydecker not only shaped the German earthquake catalogue, he also, together with his late colleague van Gils, issued the European earthquake catalogue with more than 8500 events (intensity IV and more) for the covered countries until 1906 (van Gils & Leydecker 1991). The latest addition of interest is the earthquake catalogue for southeastern Europe (Shebalin et al., 1998) with approximately 2000 events before 1906. Other important catalogues for earthquakes relevant for Bavaria are the Swiss catalogue (Swiss Seismological Service, 2002), the Austrian catalogue (Austrian Central Institute for Meteorology and Geodynamics, 2006) and the latest catalogue for central and northern Europe by Grünthal & Wahlström (2003). Between all catalogues slight discrepancies can be found, most of them regarding the precise location of the epicentre, its coordinates, the intensity and the corresponding radius. Even the Bavarian earthquake catalogue, although based on the German catalogue, shows some minor differences to the German catalogue.

Consequently all existing earthquake catalogues with possible relevance for Bavaria had to be screened in order to find more earthquake events to be included in the BASE data bank (Grünthal, 1988; Leydecker, 1986ff; Swiss Seismological Service, 2002; Shebalin et al., 1998; Austrian Central Institute for Meteorology and Geodynamics, 2006) and the Kövesligethy formula (see Equation 1) was used to determine the intensity of earthquakes from neighbouring countries. As a result all earthquakes with a calculated intensity of I ≥ 3 (with α = 0,001) for Bavaria were included.

$$\mathbf{I} = \mathbf{I}\mathbf{o} \text{-}\mathbf{3} \cdot \log(\mathbf{R}/\mathbf{h})\text{-}1.3 \cdot \mathbf{a} \text{-}(\mathbf{R}\text{-}\mathbf{h})\tag{1}$$

#### **8. The application of early seismometers**

In Bavaria the recording and scientific assessment of earthquakes is principally undertaken by the Department for Geo- and Environmental Sciences at the Ludwig-Maximilians-University of Munich and the Bavarian Environment Agency (together forming the Bavarian Seismological Service). Instrumental recording of earthquakes in Bavaria began with the 1000kg Wiechert seismometer in Munich-Bogenhausen in 1905. Today the Geophysical Observatory in Fürstenfeldbruck is the data centre for a modern digital seismological network in Bavaria.

An interesting finding when comparing pre-instrumental data with the seismographs from Bogenhausen is the difference of the geographical distribution of the earthquakes before 1905 and after. Before 1905 most earthquakes felt in Bavaria took place in either the Alps or the northern fringe of the Bohemian Forest. But a surprisingly high number of events happened all over central Europe with no apparent connection to the more active seismic regions. After 1905 we find quite a different picture, which obviously is connected to the installation of seismological stations in Bavaria, that were able to record also smaller earthquakes, "invisible" in the past. A large number of events was recorded for the Ries crater around Nördlingen, although most epicentres are still found in the Alps or the northern Bohemian Forest (cf. Barnikel & Geiss, 2008, who compare the two periods).

But even the introduction of seismometers does not mean highly precise earthquake data from that moment onwards.

Batlló (2008) points out that

*in the early XX century, fundamental concepts of seismic source physics […] were yet to be discovered, as well as the benefits of computer technology and digital signal processing.* 

#### **9. An open source project to collect earthquake information**

In order to complete the existing data base of historical earthquakes in Bavaria or relevant for Bavaria, the Bavarian Environment Agency has teamed up with the Department of Geography at the University of Munich, which offers expertise in historical assessment of natural hazards (see Barnikel & Becht, 2004). The project BASE (Bavaria's Seismicity in Historical Documents), which is currently running in its ninth year, works with historical written documents and all information about earthquakes relevant for Bavaria stored in them. The first two parts of the project (BASE I and II) dealt with the inclusion of data from already published literature, the current parts (BASE-NET and BASE20) are aiming at the inclusion of earthquake data from original written documents (letters, postcards, etc.) and the setting up of an internet website to enable interested and informed citizens of Bavaria to contribute to the data base in the future.

Of special importance in this context, when working with historical written sources, is always the exact quotation of the written texts to ensure accessibility for later evaluations. BASE links the data on the event to other researched material, like pictures or maps. The data was then compared with the data in the German and European catalogues and, if

neighbouring countries. As a result all earthquakes with a calculated intensity of I ≥ 3 (with

In Bavaria the recording and scientific assessment of earthquakes is principally undertaken by the Department for Geo- and Environmental Sciences at the Ludwig-Maximilians-University of Munich and the Bavarian Environment Agency (together forming the Bavarian Seismological Service). Instrumental recording of earthquakes in Bavaria began with the 1000kg Wiechert seismometer in Munich-Bogenhausen in 1905. Today the Geophysical Observatory in Fürstenfeldbruck is the data centre for a modern digital

An interesting finding when comparing pre-instrumental data with the seismographs from Bogenhausen is the difference of the geographical distribution of the earthquakes before 1905 and after. Before 1905 most earthquakes felt in Bavaria took place in either the Alps or the northern fringe of the Bohemian Forest. But a surprisingly high number of events happened all over central Europe with no apparent connection to the more active seismic regions. After 1905 we find quite a different picture, which obviously is connected to the installation of seismological stations in Bavaria, that were able to record also smaller earthquakes, "invisible" in the past. A large number of events was recorded for the Ries crater around Nördlingen, although most epicentres are still found in the Alps or the northern Bohemian Forest (cf. Barnikel & Geiss, 2008, who compare the two periods). But even the introduction of seismometers does not mean highly precise earthquake data

*in the early XX century, fundamental concepts of seismic source physics […] were yet to be* 

*discovered, as well as the benefits of computer technology and digital signal processing.* 

In order to complete the existing data base of historical earthquakes in Bavaria or relevant for Bavaria, the Bavarian Environment Agency has teamed up with the Department of Geography at the University of Munich, which offers expertise in historical assessment of natural hazards (see Barnikel & Becht, 2004). The project BASE (Bavaria's Seismicity in Historical Documents), which is currently running in its ninth year, works with historical written documents and all information about earthquakes relevant for Bavaria stored in them. The first two parts of the project (BASE I and II) dealt with the inclusion of data from already published literature, the current parts (BASE-NET and BASE20) are aiming at the inclusion of earthquake data from original written documents (letters, postcards, etc.) and the setting up of an internet website to enable interested and informed citizens of Bavaria to

Of special importance in this context, when working with historical written sources, is always the exact quotation of the written texts to ensure accessibility for later evaluations. BASE links the data on the event to other researched material, like pictures or maps. The data was then compared with the data in the German and European catalogues and, if

**9. An open source project to collect earthquake information** 

I = Io-3·log(R/h)-1.3·α·(R-h) (1)

α = 0,001) for Bavaria were included.

seismological network in Bavaria.

from that moment onwards. Batlló (2008) points out that

contribute to the data base in the future.

**8. The application of early seismometers** 

necessary, adjusted (with regards to time, coordinates etc.). Important for the data files are descriptions of the impact an earthquake had on the society. The more details about damages or destructions we get, the more accurate our intensity estimations will later become. Therefore, all the data have been graded after the new EMS-98-Intensity-Scale (Grünthal, 1998), which allows a direct comparison of data from different centuries and of data from different documentary sources.

Some examples of historical written data may illustrate the particular problems and chances of working with this kind of sources in the BASE-project: "In the year 740 AD the Earth trembled so much in the Swabian Countries for almost a year that many monasteries and churches collapsed" (after Gießberger, 1922). This text was found in a manuscript from 1723, therefore at least a second-hand source. Even if authors often used to simply copy older texts without changing them, a description of an earthquake almost a thousand years later is highly problematic (see Barnikel, 2004, who deals at length with this topic). The nature of the information is also doubtful. The destruction of numerous churches and monasteries (some of them certainly wooden structures as were common in these times) sounds improbable. In addition to that, no other known source recorded that many devastating earthquakes in that year in Bavaria. The validity of this source, as a result, remains very poor.

Several sources were found for a suspected earthquake in 841 AD in Würzburg (after Boegner, 1847; Gießberger, 1922; Sieberg, 1940; the mentioned sources date back to e.g. 1578, 1644, 1692 and 1756 respectively): "AD 841 an earthquake hit the town of Würzburg about twenty times and with it came terrible hail and a great storm", depicting the ancient belief that earthquakes were connected to atmospheric events. Judging from the text the event in question sounds more like a heavy storm which shook the buildings and inhabitants of Würzburg and is nowadays considered to be a fake. These "original" sources, used in the secondary sources exploited by the BASE-project, are of course hardly precise and valid, since they cannot be considered as contemporary (real contemporary sources being very rare and far between). Often sources like these make use of data already written down in older documents, thus only quoting other sources and thereby adding "new" evidence where there is none (cf. the exemplary analysis of a series of earthquakes in southern Germany found to be fakes by Grünthal & Fischer, 2001), or just mix up the dates, as is the case with earthquakes listed after either the Julian or the Gregorian calendar (as for example Grünthal & Wahlström (2003) point out; also see chapter 5).

Much more precise and valid in general are understandably younger documents, one example being an earthquake in 1889: "On February 22nd, 2 o'clock and 40 minutes in the afternoon, a heavy blow sounded, which was accompanied by a short rolling sub-surface, so that the windows clattered in many houses. This blow seemed to move from W to E. In the lower part of town the same was felt so heavily that the inhabitants of the surrounding streets ran terrified onto the streets." This information appears not only much more reliable, it is also very precise in terms of date, time, place, process and effect. It is especially this kind of source we need to specify an earthquake.

The BASE-project so far was able to collect a total of 516 events which were perceived and, consequently, recorded in Bavaria. Astonishing enough is the fact that about 76% of these events could not be linked to a specific date or place from the earthquake catalogues of the surrounding areas (the European earthquake catalogue by van Gils & Leydecker (1991) or the German earthquake catalogue by Leydecker (1986ff.), although quite a few events must be considered fakes, especially when just mentioned by a few (or only one) sources. Only 122 earthquake epicentres in addition to the 24 events already listed in the Bavarian earthquake catalogue could be specified. Most of these events took place in either Switzerland (23%) or Austria (16%), just under 10% in the German state of Baden-Württemberg, the Czech Republic or Italy respectively. The large number of uncertain epicentres for earthquakes felt in Bavaria is nevertheless puzzling, but so is the fact that both, the German and the European catalogue, list a significant different number of German quakes with the same intensity span for the time period up to 1905. The European catalogue mentions 1019 events in Germany before 1906, the German catalogue 1821.

In total a number of 1673 references to earthquakes in Bavaria for the time up to 1905 have been collected. For these references date, time, location, quotation, details about the earthquake itself, damages and other crucial information are listed in the data base. The exceptions are of course those earthquakes which have been extracted from maps, where no further information from within Bavaria could be found. These earthquakes are attributed to their origin outside Bavaria and are listed in the data base under the names of Bavarian cities and towns on the maps.
