A New Catalogue of Historical Earthquakes in the Corinth Rift , Central Greece: 480 B.C. - A.D. 1910
This is Chapter 2, First Part, the Main Events New Catalogue of the book Historical Earthquakes and Tsunamis in the Corinth Rift, Central Greece, G.A. Papadopoulos (Ed.), Publication No. 12, Institute of Geodynamics, National Observatory of Athens, 129pp., Athens, 2000.
The book includes a set of another three Chapters as follows:
Chapter 1: Editorial
Chapter 2: consists of the present explanatory text and the New Historical Earthquake Catalogue.
Chapter 3: A New Tsunami Catalogue of the Corinth Rift:373-B.C.-A.D.2000
Chapter 4: An Unknown Historical Earthquake in the Fili Region?
For further information about the book please contact with
Dr G.A. Papadopoulos
Institute of Geodynamics
National Observatory of Athens
11810 Athens , Greece
A New Catalogue of Historical Earthquakes in the Rift of Corinth, Central Greece
G.A. Papadopoulos * , A. Vassilopoulou and A. Plessa
Institute of Geodynamics , National Observatory of Athens, 11810 Athens, Greece
The region covered by the New Earthquake Catalogue is that of the Corinth Rift as it defined in Chapter 1 of the present volume. The catalogue covers the time interval from the 5th century B.C. to the A.D.1910 inclusive because from 1911 onwards a systematic instrumental monitoring and recording of the Greek earthquakes started by the Institute of Geodynamics, National Observatory of Athens (NOAGI,) after the installation on 1910 of a good-quality Mainka type seismograph .
Thanks to the data sources used and the method of data analysis applied (see section "IV. Method"), we were able to identify not only main events but also dependent events, that is foreshocks and aftershocks associated with some of the main events . The long aftershock sequences associated with particular large earthquakes occurring in the Corinth Rift during the 19th century were already noticed by the end of that century. For example, Mitzopulos (1893) reported on that the aftershock sequence of the 1 August 1870 large shock lasted for about three years.
The New Earthquake Catalogue consists of four main parts: the First Part is the Main Events New Catalogue, the Second Part consists of the Dependent Events New Catalogue, the Third Part contains documentation and some additional material, while further reading and a list of references is included in the Fourth Part .
II. Data Sources for the New Earthquake Catalogue
A variety of data sources has been collected and examined: texts of ancient writers,
chronicles, travellers reports, anonymous reports, earthquake files, books, previous catalogues and modern scientific publications. Of particular interest are four different data sources that were not utilized, or were only partly taken into account, by previous researchers. Three of them, refering in general to the Greek seismicity and, therefore, include the Corinth Rift, cover three sequential periods of the time interval from1850 to 1910 inclusive, while the fourth one covers only the particular area of Galaxidi for the time interval from 996 to 1660.
The first source consists of two books of Schmidt (1875,1879) where a detailed list of even small earthquake events, that occurred in Greece from 1850 to 1878 inclusive, can be found. The operation of Julius Schmidt at the position of the Director of the National Observatory of Athens (NOA) started on December 1858 and terminated on February 1884. Soon after his operation started , J. Schmidt organized a system of local observers in several places of the already liberated part of Greece that included the geographical region of the Corinth Rift. The observers were educated persons, like medical doctors or school teachers, keeping daily reports on earthquakes felt in the particular places of their residence. This information was sent to NOA and systematic earthquake files were organized by J. Schmidt and his collaborators who were also checking and correcting the time of the earthquake occurrences. Additional earthquake information was collected from the press. This procedure resulted in the compilation of a very long, highly homogeneous earthquake catalogue containing not only strong earthquakes but also events of even small size. For each event the date and time of occurrence as well as a short description of the felt intensity are listed in the books of J. Schmidt. For strong and large events some further details about their impact are given .
On the basis of a systematic newspaper reading , Galanopoulos ( 1953) completed the work of J. Schmidt for the time interval 1879 - 1892. This publication constitutes the second important data source for earthquake events of mainly medium and small size.
The third data source that diserves particular attention consists of two manuscript volumes of NOAGI listing earthquake events that occurred in Greece in the time interval
1893 - 1901 (Anonymous , a) and 1902 - 1915 (Anonymous, b) . The volumes, written in Greek, contain observational material based also on local observers and press reports, and arranged in the format the catalogue of Schmidt is prepared . Since 1898 primitive seismic instruments of Agamennone type started to operate in Greece and, therefore, information on recording parameters, like first arrivals, are contained for some events of the period 1898 - 1915. For each one event an indication of the intensity felt is listed as well. However, for strong and large earthquakes detailed macroseismic descriptions are included. It is worth noting that for the time interval 1893 - 1897 only qualitative intensity indications or descriptions are given, while for the post-1987 time interval quantitative intensity estimates are also supplied. The macroseismic scale used is a version of the Forel Scale which is displaced in Greek at the end of the manuscript volume of Anonymous ( b ) . In the Third Part of the present Chapter a reproduction of the Forel Scale description, exactly as it stands in Anonymous ( b), along with an English translation made by us, can be found.
The raw observational material included in Anonymous (a ,b ) , after some corrections , elimination of details and editorial standardization , was published in French in the Bulletins of NOA (BNOA) under the title " Annales de l' Observatoire National d' Athenes" supervised by D.Eginitis, NOA Director for the period from June1890 to March 1934. The fact that we were able to examine the original source of information , that is the two manuscript volumes of Anonymous (a,b), on which the earthquake information contained in BNOA Bulletins is based on, has been of special value for the evaluation of the earthquake observational material collected for the time interval 1893 - 1910. From 1904 onwards the macroseismic scale used in BNOA is the Rossi-Forel scale. The version of this scale used is not included in Anonymous (b) or BNOA. We suggest that it was the version of 1883 (e.g. Sieberg, 1923).
The fourth data source that diserves special attention is the "Unpublished Chronicle of Galaxidi". Én this book, Sathas (1865) published the monk's Efthimios manuscript entitled "A History of Galaxidi" written in Galaxidi in 1703 . Several editions of the book followed in more recent times, the most recent of them being the edition made in Athens by Charisis (1996). A comparison of the editions of 1865 and1996 made by us indicated that there is no any discrepancy as for the reproduction of the manuscript.
The above mentioned manuscript is of improtance from seismological point of view because it contains information about four earthquake events occurring in the area of the town of Galaxidi, in the central part of the Corinth Gulf, from A.D.996 to A.D.1660. However , it is not clear whether all the earthquake events described by the monk Efthimios in his manuscript were or not real earthquake events .We evaluated this information and our result is reflected in the reliability scores assigned to each one of the above four earthquakes (see Main Events New Catalogue, First Part of this Chapter) as well as in the section "Comments on Some Particular Earthquakes" that can be found in the Third Part of this Chapter.
III. Structure of the New Earthquake Catalogue
The New Earthquake Catalogue consists of the Main Events New Catalogue and
the Dependent Events New Catalogue contained in the First Part and the Second Part of this Chapter, respectively. Both the New Catalogues are arranged in a chronological order . The earthquake parameters introduced and the respective symbols used in the New Catalogues are explained in section "IV. Method". As already mentioned above, the New Earthquake Catalogue is supported by documentation and some additional material in the Third Part of this Chapter, which includes the Forel intensity scale used by Anonymous (b), original documentation for some particular earthquake events, a commentary on events not included in the New Earthquake Catalogue , a list of earthquake events identified by archaeological and palaeoseismological methods, some pictorial material, as well as previous cataloguing of both the main and dependent events. The New Earthquake Catalogue is also supported in the Fourth Part of this Chapter by a list of further reading, a key of references used in both parts of the New Earthquake Catalogue and a list of all references cited in the present volume.
IV.1. Material Used
For each earthquake event listed in either the Main Events New Catalogue or the Dependent Events New Catalogue we collected information from various data sources and created two different files . File A lists sets of earthquake parameters determined by previous authors (see Third Part of this Chapter).The inclusion of this material makes easier the evaluation of the earthquake parameters determined by previous authors for one and the same event. It is understandable that more than one sets of parameters correspond to each particular earthquake event because, as a general rule, more than one authors dealt with the parametric description of each event. File B consists of the original descriptions of the respective event . For most of the strong events (maximum intensity I ? VI) original descriptions have been published by other authors, like Ambraseys and Finkel (1992, 1993) and Ambraseys (1996) for the 1705 earthquake, Ambraseys and Finkel (1999) who supplied Ottoman archival information on several earthquakes of the time period from 1500 to 1800, Georgiades (1904) for the time period from 12000 B.C. to the Birth of Christ, Guidoboni et al. (1994) for several earthquakes that occurred before the year A.D.1000, ,Papadopoulos (1998) for the 373B.C. event. However, for some of the strong events original documentation has not been internationally accessible so far and , therefore, we decided to include the respective material in the Third Part of this Chapter.
IV.2 Events Listed
All the earthquake events reported in the several data sources examined for the time interval from the beginning of the catalogue, that is from 480 B.C., to 1849 inclusive are listed in the New Earthquake Catalogue. Those events were strong ones given that the maximum intensity , I , assigned to most of them , in the modified Mercalli-Sieberg or the Forel Scale, is of degree VI or larger . However, for some particular cases intensity I has not been introduced in the New Earthquake Catalogue because of data inadequacy. From about 1800 onwards, however, the reporting capabilities increased drastically, in particular from about 1850 onwards, thanks to the observation activities undertaken by the newly established NOA. Therefore, a long number of seismic events of I < V were introduced in the earthquake lists, thus often creating confusion as for the place(s) each event was reported from. As a consequence, in the Main Events New Catalogue we included only events of I ? V . However, in the Dependent Events New Catalogue we were able to include shocks of I < V.
In the Dependent Events New Catalogue the selection of foreshocks, if any, was a rather easy task because they were only a few and did not occur for a long time before the respective main shock occurrence. A more painful procedure has been the aftershock selection. In several cases their number was very long and the aftershock sequence lasted for several months or even for a few years (e.g. the aftershock sequences of the large main shocks of 26th December 1861 and 1st August 1870, code numbers 61 and 68 in the Main Events New Catalogue , First Part of this Chapter, respectively). In these cases the selection has been in a way that the sequence roughly conforms with the Omori law for the exponential decrease of the number of aftershocks with time. It is understood that some events may have erroneously introduced as aftershocks of a particular main shock and that some others possibly did not considered as aftershocks although they indeed were. Nonetheless, the very carefull selection we made guarantees that the possible mistakes introduced do not affect the general value of the Dependent Events New Catalogue and of each one of the sequences included in it. Before introducing in the New Earthquake Catalogue an event strongly felt in place(s) of the Corinth Rift we checked for the possibility of having its origin outside the Corinth rift. In view of this some events were excluded from the New Earthquake Catalogue (see examples in section "Third Part: Documentation and Additional Material" of this Chapter.
IV.3 Earthquake Parameter Determination
The construction of the New Earthquake Catalogue in a parametric form has been made under three main rules: ( a ) A particular earthquake parameter , like time of occurrence , epicentral coordinates, maximum intensity felt, Richter magnitude and focal depth, is introduced in a particular earthquake event only when it is justified by the available observation data; otherwise we prefered to leave blank the respective entry. ( b ) When a particular parametric value has been introduced then it is the "best" value that has either selected from one of the existing previous catalogues or determined by us. Therefore, the New Earthquake Catalogue constitutes an amalgamation of the best output of our new determinations and of previous catalogues . ( c ) In our determinations we often prefered rather to indicate value intervals of the form " equal to or larger (smaller) than…" than to determine a single value not well justified by the observation data.
IV.3.1 Time of Occurrence and its Reliability
The earthquake parameters adopted in the New Earthquake Catalogue were decided on the basis of a two step procedure. In the first step we relied on Files A and B to control the justification of the time and place of occurrence for each particular event. With this procedure we were able to correct the time and the place of earthquake occurrences, to avoid dublications and false entries and to control possible time and place inconsistencies between the different sets of earthquake parameters given in different catalogues in the past. At the same time for each event we were able to identify the Accuracy (Acc) or the error involved in the time of occurrence. An effort has been made to provide dates in the new style (Gregorian) . Nevertheless, in some particular cases it is not clear whether or not in the original documents the earthquake dates are given in the old (Julian) or in the new style.
IV.3.2 Epicenter, Maximum Intensity, Richter Magnitude, Focal Depth
The second step was devoted to the determination of the earthquake epicenter , the maximum intensity reported and the Richter magnitude of the event. We first examined
File B for whether the parameters determined by previous authors are justified or not by the original documents . In cases of positive conclusion we accepted for the New Earthquake Catalogue parametric values already given by someone of the previous authors. For some particular events, however, different parameter determinations were adopted from different authors. In cases that according to our understanding the parameter determinations were not justified by the original ducumentation we redetermined the parameters and they were introduced in the New Earthquake Catalogue. As for the earthquake epicenters of strong events, in general we adopted those listed in someone of the previous catalogues with only very few exceptions. However, a large number of moderate and small earthquake events are reported only from a very limited number of observation localities. Then , the macroseismic information available is not adequate to support a reliable epicenter determination and , therefore, we conventionally indicate in parenthesis the geographical coordinates of the region where the maximum intensity, I , was reported.
The maximum intensity and the Richter magnitude assigned to several earthquake events have also been adopted by previous author(s). In a considerable number of events, however, we considered that the past intensity and / or magnitude determinations were not justified by the original observational material available and , therefore, those determinations were not adopted. Instead, we either redetermined the respective parameter(s) or avoided to do so because of data inadequacy. In our intensity and magnitude determinations we often prefered rather to indicate value intervals of the form " equal to or larger (smaller) than…" than to determine a single value not well justified by the observation data.
The focal depth of the earthquakes listed in the New Earthquake Catalogue is assumed to be shallow given that it is the general rule for the Corinth Rift earthquakes as it results from the modern seismograph data. Only the large event of 25th August 1889 (code number 87 in the Main Events New Catalogue ) was suggested by previous authors to have been of intermediate focal depth. According to our opinion, however, the large number of aftershocks felt indicate a shallow focal depth for this event.
IV.3.3 Event Reliability
A reliability score, Rel, for a particular earthquake of being a " real earthquake" event or not has been introduced in the New Earthquake Catalogue. Rel is measured in a scale ranging from 0 to 4 and constructed in a way to represent probability for a real earthquake occurrence or for a false earthquake reporting:
0: very improbable event
1: improbable event
2: questionable event
3: probable event
4: definite event
This approach was developed by Iida (1984) for the creation of a tsunami reliability scale in Japan and adopted with minor modifications by the GITEC group working on the new European Tsunami Catalogue (see Chapter 3). The criteria applied to assign Rel to each event were the number of independent sources reporting the event, the credibility of each one of the reporting sources as well as the consistency between the several sources. Events assigned with a 0 were not included in the New Earthquake Catalogue.
IV.4 Symbol Key to the New Earthquake Catalogue
The Symbol Key contained in this section is the same for both the Main Events and the Dependent Events New Catalogues.
ID : code number
An effort has been made to provide dates in the new style (Gregorian)(see section "IV.3.1").
hh: hour (UT)
Acc: accuracy of the time of earthquake occurrence.
Acc usually refers to the last entry of time. However, if it is followed by Y, M, or D then it refers to the respective entry that is to Year, Month or Day. Acc is measured in units of the respective time entry . For instance, in the event of ID =3 (First Part of this Chapter, Main Events New Catalogue) the Acc = 0 means that the time accuracy is on the order of one month, while in the event of ID = 12 it is on the order of two years. In the event of ID = 1, however, Acc is on the order of 30 days.
lat:geographic latitude of epicenter
long: geographic longitude of epicenter
The epicentral coordinates are given without parentheses when adopted by other authors.
Coordinates in parentheses indicate only the place of the maximum intensity felt. This option has been prefered when either we did not adopt determinations of other authors or the data available were inadequate for an epicenter determination.
I : maximum intensity in MM (modified Mercalli-Sieberg scale ) unless otherwise indicated (F = Forel scale, RF = Rossi - Forel scale)
M: Richter magnitude equivalent to surface-wave magnitude
h: focal depth (in km)
n: shallow event
All the events listed are suggested to be of shallow focal depth given that we have no evidence for a particular event to be of intermediate focal depth. For reasons of emphasis symbol n is placed only in the case of the ID = 87 event (First Part of this Chapter, Main Events New Catalogue) which has been particularly discussed in section " IV.3.3".
Rel: reliability of the event (see scale of reliability in section "IV.3.2")
Ref 1: references used for the adoption of earthquake parameters including time of occurrence
Earthquake parameters are either adopted by other authors or revised by us ( see section "IV. Method" ).
( + ) after a particular value means "equal to or larger than"
( - ) after a particular value means "equal to or less than"
* indicates parameter either determined or revised by us
- before the year of occurrence means "Before Christ"
c after the year of occurrence means "circa".
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