Fig. 1 - Flow-chart of the project.
1 - Objectives and expected
achievements
1.1 - Goals
The main goal of the project is to prepare a basic earthquake catalogue of Europe, to serve both as a tool for understanding the long-term seismicity and as a reliable input for seismic hazard evaluation.
The most recent achievements have shown that the only way to produce a reliable,
comprehensive catalogue is to prepare first a database of primary data, from
which one or more catalogues can be compiled according to the criteria suggested
by the users. Therefore, in order to achieve the main goal, a database
of primary data (macroseismic and instrumental observations) will be
prepared. This task will be performed in two steps:
- retrieving, evaluating and making available, according to a standard format, the considerable body of data existing in published and - mostly - unpublished studies;
- investigating, according to standard criteria, the main earthquakes for
which no primary data is available.
Starting from the database of primary data, a catalogue will be compiled
using rigorous and transparent procedures.
Basic. The compilation of a complete European earthquake catalogue may involve the analysis of several tenths of thousands of entries, which is far from the real possibilities of a two-years project. Therefore, the project will mostly concentrate on the earthquakes which are essential for hazard assessment, that is, on the largest earthquakes with respect to the seismicity of each area.
European. By "Europe" it will be meant hereafter the territories of the countries belonging to EC and neighbouring areas. Actually, for the assessment of seismic hazard of Europe it is necessary to take into consideration also the seismic sources which lie outside EC, but which can affect its territory. Therefore, the investigation will cover also large earthquakes, the epicentral areas of which do not fall within EC frontiers but which have significantly affected EC countries.
Long-term. By "long-term" it is meant as far back as the data allow:
however, it seems reasonable to expect a good, overall coverage over the
last five centuries. The data potential for the Middle Ages and before is
not uniform throughout Europe: a comprehensive review of this time-window
would require heavy historical investigation and is likely to be extremely
time and effort consuming, and to produce a badly incomplete set of data,
difficult to interpret. Therefore, this time-window will be considered with
low priority.
1.2 - Methodology
1.2.1 - Main problems. Though very useful for computational purposes, most available parametric catalogues suffer from many problems.
First of all, most catalogues have been compiled on a national basis: it happens, therefore, that even important earthquakes, the epicentres of which fall slightly outside the national boundaries, are not included in the national catalogues even if they have affected the national territory; therefore, sometimes they are not taken into account for hazard evaluation.
Furthermore, the epicentral location of an earthquake, as given by a catalogue, may considerably differ from that of the neighbouring country. Therefore, any choice among two or more catalogue records referring to the same event is likely rather casual if performed without checking the primary data.
The most serious problems come from transfrontier earthquakes. Many catalogues are full of duplications coming from careless handling of data. As for historical ones, this is mostly due to chronological and/or geographical errors and there is no other way to sort them out, other than to reconsider the primary data. Similar problems apply also, though less frequently, to instrumental data. In order to overcome these problems, the project will:
- retrieve the datasets (intensity datapoints or even historical records for the macroseismic data, onset times or even waveforms for the instrumental ones) from which catalogues have been derived;
- evaluate and, if necessary, improve them;
- merge them to produce a new, comprehensive dataset, from which a new set
of earthquake parameters will be derived.
1.2.2 - Main steps. The project will develop according to the following
steps, (Fig.1):
1.2.2.1 - retrieval and evaluation of the existing parametric catalogues: compilation of a working file;
1.2.2.2 - retrieval and evaluation of the existing sets of primary data;
1.2.2.3 - data investigation for the improvement of the datasets;
1.2.2.4 - compilation of a comprehensive dataset;
1.2.2.5 - catalogue compilation, after selection and implementation of procedures
for the determination of earthquake parameters.
Fig. 1 - Flow-chart of the project.
1.2.2.1 - Working file. A "working file" will be compiled by merging the national/regional parametric catalogues adopted: in the working file, all records related to the same earthquake will be preserved, without any a-priori selection.
As a next step, a selection of the main earthquakes will be performed: just to have a preliminary idea of the amount of earthquakes to be dealt with, the current catalogue of Van Gils and Leydecker (1991) includes, in the portion East of 0°, 509 earthquakes with Io _ 7/8 South of 47° N, and 193 earthquakes with Io _ 6/7 North of 47° N. Dropping, as a preliminary selection, all earthquakes included in a time-space-window of ± 90 days and ± 30 km around the major events, the two figures are reduced to 365 and 144 respectively. To these figures, earthquakes located West of 0°, those in the Balkans and in the other countries sorrounding CEC are to be added.
The working file will only serve as a tool for the next operations: the final
catalogue will be produced after the investigation described below.
1.2.2.2 - Primary datasets. A survey of all the existing data referring to the earthquakes listed in the working file will be performed in order to inventory, analyse and, if necessary, re-compile them according to the same standard. This task will be undertaken in a systematic way: therefore, one of the main purposes of this project will be to survey the published, unpublished or little known materials which have served for the compilation of the existing catalogues.
At the same time, criteria for the evaluation of the quality of the information will be established (for instance, for the macroseismic data, type of sources, number and distribution of observations, reliability of intensity assessment), in order to point out whether the data meets the required standard or, on the contrary, further investigation is needed.
The survey will point out three classes of events:
a) earthquakes for which primary data, of sufficient quality, are available;
b) earthquakes for which primary data are available, but need to be improved;
c) earthquakes for which no primary data are available.
Earthquakes of class b) and c) will be investigated in order to be upgraded
to class a).
1.2.2.3a - Macroseismic data investigation. Macroseismic data comes
from the elaboration of historical records or questionnaires. In principle
they could be processed according to the same procedures as instrumental
data: however, macroseismic procedures, still rather personal, often lead
to inhomogeneous catalogues. In order to satisfy a minimum standard, macroseismic
data need to be homogeneous with respect to:
- historical investigation;
- timing criteria, locality denominations and coordinates;
- intensity scale;
- procedures for the determination of earthquake parameters.
a) Historical investigation.
The problem of how historical records are retrieved, interpreted, assembled and how their reliability is evaluated is of primary importance for the quality and the homogeneity of a catalogue. It is well known, for instance, that presumed seismic gaps can be explained by historical source gaps and that poor information can be simply due to non-exhaustive investigation.
It has already been recalled that most historical catalogues currently in use still follow from massive parameterization of classical seismological compilations (such as Perrey, Sieberg, etc.). These are, in their turn, the result of historical investigation performed according to varied criteria: therefore, the reliability of the catalogues derived from them is also quite varied.
As a minimum, standard level, the sources used by the most reliable seismological
compilations will be retrieved and investigated, in order to make clear and
evaluate the background of the parameters included in the catalogues.
b) Timing criteria, locality denomination and coordinates.
Timing carried by historical records is usually expressed according to various calendars or time-systems: furthermore, the timing of the records referring to the same earthquake can be scattered along a large time-span; therefore it is a decision of the investigator to assign them the same origin time The same problems exist in principle for locality denominations, and it can be very complicated by the change of names and coordinates and by non-explicit interpretations of the investigators.
In order to keep a trace of the decisions assumed, intensity data will be
compiled in such a way to carry both the original and the given time;
furthermore, locality names and coordinates will be expressed according to
directories, and a trace will be kept of the original input names.
c) Intensity scale.
Intensity assessment is still an important reason for inhomogeneity: intensity data is usually expressed in terms of different scales, often not even specified. However, it is nearly impossible to re-assess intensity in a homogeneous way in a short time for all macroseismic observations to be considered. Nevertheless, the publication of the new EMS (European Macroseismic Scale) gives a good opportunity for reconsidering this problem with special care.
Attempts will be made in order to assess the new intensity data according
to this scale and to correlate the existing data with it.
1.2.2.3b - Instrumental data investigation. The study of the largest
European earthquakes of the 20th century will be performed joining the
macroseismic investigation to the recomputation of instrumental parameters.
These data will allow the determination of calibration functions for describing
pre-20th century earthquakes in the same way as in the instrumental period
and/or, at the same time, the use of more sophisticated computer programmes
for seismic risk analysis, generally working in terms of magnitude.
The development of this part of the project will require the re-evaluation of:
- hypocentral location (mainly for off-shore events; the relocation will be mostly accomplished using original seismograms, as well as bulletin data if waveforms are missing);
- source mechanism (from original waveforms and only exceptionally from station bulletins);
- magnitudes (Ms, mb, Maw, from world-wide station bulletins and, when possible, from original seismograms);
- seismic moments (by compiling and checking the published data).
Among the above mentioned parameters, special care will be paid to earthquake
location and to the re-assessment of surface wave magnitudes (Ms); in fact,
Ms is the only parameter determined in a standard way (earthquakes with M
> 3.5 Æ 4).
1.2.2.4 - Compilation of a comprehensive dataset. All primary data,
original or improved, will be stored in a single, comprehensive dataset,
organised in such a way to recognize original entries and to allow multiple
queries and elaborations. In order to store the data, a database will be
organised in such way not to disregard any valuable information, to allow
the user to retrieve data easily (by geographic location, by date of the
event sought) and to navigate through the data sets. The database will be
organised in close correlation with the philosophy of the seismological database
"MEDEA".
1.2.2.5 - Catalogue compilation. Current catalogues are very inhomogeneous with respect to how earthquake parameters were inferred from macroseismic data: therefore, the quality of a catalogue can be improved by determining earthquake parameters according to standard procedures. Actually, procedures for assessing earthquakes parameters are well defined for instrumental data, but not for macroseismic data; with reference to this problem, a survey of the current methods of earthquake parameters determination from macroseismic data will be performed and the most suitable one will be implemented in the perspective of seismic hazard assessment.
At the end of the investigation, a new catalogue will be compiled for all events from the corresponding dataset, according to the procedures described before. The records will be stored under a format which will guarantee the maximum information useful for hazard assessment. When both instrumental and macroseismic data are available, two separate records will be stored, adding a flag to point out that they deal with the same earthquake.
New records will be added to the working file and relationships will be specified
between new and old records, in order to make clear to the user the evolution
achieved. The compilation procedure will be organised in such a way to keep
a trace of all steps and decisions performed; this will allow to upgrade
easily any record as soon as the corresponding data will have improved.
1.3 - Milestones
| months from commencement | |
| Working file | 3 |
| Primary datasets | 9 |
| Data investigation | 18 |
| Comprehensive dataset | 21 |
| Catalogue | 24 |
2 - Role of participants
In order to retrieve and put together the huge amount of material on the largest European earthquakes the contribution of many institutions is required. This is the reason for having a high number of participants: in principle it would need to be even higher, and volunteer collaboration will be searched for.
Most participants will share the main part of the project, that is the data
investigation, on a geographical basis, each one of them taking care of different
regions. The tasks will be shared as follows:
Contractors:
01 - Consiglio Nazionale delle Ricerche (CNR), Milano, will coordinate
the retrieval and merge of the macroseismic datasets; re-evaluate the earthquakes
of Italy and Western Iberia; organise the data management and the catalogue
compilation. CNR will benefit from the collaboration of J. Vogt and J. Bonnin,
and arrange the collaboration of the European-Mediterranean Seismological
Centre (EMSC).
02 - GeoForschungZentrum (GFZ), Potsdam, will be responsible for
collecting and evaluating data of earthquakes concerning Germany, Austria
and Northeastern Europe.
03 - Imperial College of Science and Technology (ICST), London,
will be responsible for re-evaluating earthquakes in the Balkans and
for the calibration of instrumental magnitudes.
04 - Osservatorio Geofisico Sperimentale (OGS), Trieste, will
be responsible for collecting and evaluating earthquake data of Central Eastern
Europe and will benefit of the collaboration of the Seismological Surveys
of Ljubljana and Zagreb.
05 - University of Athens (NKUA), Athina, will be responsible for
collecting and evaluating data of earthquakes of Greece and surrounding
countries.
06 - Servei Geologic de Catalunya (SGC), Barcelona, will be responsible
for collecting and evaluating data of earthquakes of Catalonia and
Pyrenees.
Associated contractors:
07 - Schweizerische Erdbebendienst (SED), Zürich, associated
to GFZ, will be responsible in retrieving and evaluating earthquake data
in the Alpine region.
08 - British Geological Survey (BGS), Edinburgh, associated
to ICST, will be responsible for collecting and evaluating earthquake data
of Northwestern Europe.
09 - Istituto Sperimentale Modelli e Strutture (ISMES), Bergamo, associated to OGS, will collaborate in the compilation of working file, datasets and catalogue.
3 - Deliverables and work schedule
Deliverable 1 - Catalogue.
The homogeneous, basic catalogue of the main European earthquakes
which have affected the territories of CEC countries in the last 500 years
will be compiled under a computer format which will be at the same time
compatible with the current codes for hazard evaluation and with the exigence
of providing users, directly or undirectly, with all background information,
containing references to the database.
Deliverable 2 - Primary data.
The main content of the primary dataset for the aforementioned main earthquakes,
as retrieved from the existing studies and from the investigation carried
out in the frame of the project, will be compiled and delivered as a computer
database.
Work schedule.
The five tasks will be carried out according to a slightly overlapping sequence.
Fig. 1 shows the PERT chart of the project, including the manpower dedicated
to each task. Three general meetings (M1, M2, M3), a progress report (PR)
and a final report (FR) are foreseen.
R1 = first annual report
R2 = second annual report
PR = progress report
FR = final report