# 1921–2021: 100 years of macroseismic studies at BCSF

Christophe Sira, Michel Cara, Antoine Schlupp, Frédéric Masson, Marc Schaming, Véronique Mendel

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Christophe Sira, Michel Cara, Antoine Schlupp, Frédéric Masson, Marc Schaming, et al. 1921–2021: 100 years of macroseismic studies at BCSF. Comptes Rendus. Géoscience, 2021, 353 (S1), pp.1-29. 10.5802/crgeos.87. hal-03516813

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<figure><img src="image_1.png" /></figure>
# Comptes Rendus
## Géoscience
### Sciences de la Planète

Christophe Sira, Michel Cara, Antoine Schlupp, Frédéric Masson, Marc Schaming and Véronique Mendel

**1921-2021: 100 years of macroseismic studies at BCSF**

Online first, 23rd November 2021

<https://doi.org/10.5802/crgeos.87>

**Part of the Special Issue:** Seismicity in France

**Guest editors:** Carole Petit (Université de Nice & CNRS, France), Stéphane Mazzotti (Univ. Montpellier & CNRS, France) and Frédéric Masson (Université de Strasbourg & CNRS, France)

© Académie des sciences, Paris and the authors, 2021.

Some rights reserved.

<figure><img src="image_2.png" /></figure>

This article is licensed under the

CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL LICENSE.

http://creativecommons.org/licenses/by/4.0/
Seismicity in France / Sismicité en France

# 1921-2021: 100 years of macroseismic studies at BCSF

Christophe Sira<sup>a, *, a</sup>, Michel Cara<sup>b</sup>, Antoine Schlupp<sup>a, b</sup>, Frédéric Masson<sup>a, b</sup>, Marc Schaming<sup>a, b</sup> and Véronique Mendel<sup>a</sup>

<sup>a</sup> Université de Strasbourg, CNRS, EOST UMS 830, Strasbourg F-67084, France

<sup>b</sup> Université de Strasbourg, CNRS, ITES UMR 7063, Strasbourg F-67084, France

E-mails: christophe.sira@unistra.fr (C. Sira), michel.cara@unistra.fr (M. Cara), antoine.schlupp@unistra.fr (A. Schlupp), frederic.masson@unistra.fr (F. Masson), marc.schaming@unistra.fr (M. Schaming), veronique.mendel@unistra.fr (V. Mendel)

**Abstract.** The French Central Seismological Bureau (BCSF) was set up in Strasbourg in July 1921 by a governmental decision. Since then, BCSF is in charge of the macroseismic survey for the French territories. One of its main tasks is to determine macroseismic intensity in the different localities after each felt earthquake. This paper shows how the way of collecting macroseismic information evolved with time through the analysis of questionnaires sent to various dissemination networks and by using different methods and macroseismic scales. In context of a renewal of interest in macroseismic data, we present their main uses, as well as some perspectives for the forthcoming years. The quality of macroseismic data, together with the improvement of the analytical methods and the accessibility to BCSF data, in particular those from our archives, remain at the heart of our concerns and objectives.

**Keywords.** Macroseismic survey, Intensity, Macroseismic questionnaire, Seismic hazard, Ground motion, Historical archives, Earthquake.

Online first, 23rd November 2021

## 1. Introduction

Before the advent of instrumental seismology at the end of the XIXth century, knowledge of earthquake phenomena was based entirely on the analysis of macroseismic effects of past earthquakes. In France, the first macroseismic survey may have been conducted in 1783 by the Academy of Dijon for an earthquake in Burgundy [Schlich, 1984], and earthquake catalogues published by Alexis Perrey (1807-1882) have been the main source of information for years

[Fréchet, 2008]. Indeed, at the beginning of the XXth century, very few instrumental data were available. Promoting the installation of new seismographs and facilitating international exchange of the data was then a major challenge for seismologists. For this purpose, Georg Gerland, professor of Geography at the German University of Strasbourg, promoted the idea of an international association of seismology [Rothé, 1981]. The association officially started in 1904 with its central Bureau at the University of Strasbourg (Bureau central de l'association internationale de sismologie (BCIS)).

At that time, seismology was much less developed in France than in other European countries

<footnote>* Corresponding author.</footnote>
like Germany, where Strasbourg was located until
1918, Italy, or the United Kingdom. In 1909, during
the third meeting of the permanent commission of
BCIS, the recently appointed director of the French
"Bureau central météorologique" (BCM) in Paris, Al-
fred Angot, announced the May 23, 1908, govern-
mental decision, creating a seismological service for
"France and its colonies" [Angot, 1909]. Its seismo-
graphic station was fixed in Parc St Maur near Paris,
while stations were already functioning in the cities
of Besançon, Marseille, Toulouse, Lille, and in Puy-
de-Dôme near Clermont-Ferrand. A 7th station was
also planned to be installed in Algiers. The Lambesc
(Provence) June 11, 1909 earthquake was the op-
portunity of launching the first large BCM macro-
seismic survey made with questionnaires [Angot and
Lemoine, 1910, Fréchet, 2008]. By "questionnaire" in
the text, we mean a document that allows you to an-
swer a series of open-ended, semi-open-ended, or
tick-box questions (more contemporary version of
survey questionnaire).

In 1919, at the end of World War I, Edmond Rothé
took the chair of geophysics at the new French Uni-
versity of Strasbourg. He became responsible for both
the international association and its central Bureau.
The former BCM seismological service was moved to
Strasbourg and the French government decided on
July 28, 1921, the creation of the "Institut de Physique
du Globe de Strasbourg" (now "Ecole et Observatoire
des Sciences de la Terre" (EOST)) and its "Bureau
central sismologique pour la France et les colonies"
(BCSF).

Since 1921, macroseismic questionnaires are col-
lected by the BCSF, except during a few years be-
tween 1978 and 1986 when the French "Bureau de
recherches géologiques et minières" (BRGM) was in
charge of this task [Roger, 2021]. These question-
naires were fulfilled by local authorities and/or indi-
viduals after each felt earthquake. Observations de-
rived from this macroseismic information (intensi-
ties) and mixed with instrumental seismicity are pub-
lished in different forms and in a more or less homo-
geneous way between 1920 and 1970.

Considering the renewal of interest in macro-
seismic data for seismic hazard investigations, the
present paper aims at summarizing how macro-
seismic observations were collected and have
been processed in France by BCSF over the past
100 years.

## 2. Macroseismic scales

Effects of an earthquake on persons, objects, build-
ings, and sometimes on the natural environment, are
commonly evaluated in terms of macroseismic in-
tensity, an indicator that characterizes the severity
of the seismic ground shaking in a given restricted
area. By convention, intensity is expressed by an in-
teger number written in Roman letter. Macroseismic
scales are the tools allowing any analyst to fix the in-
tensity degree in a conventional way. Before 1921, the
10-degree Rossi-Forel scale [De Rossi, 1883] was the
macroseismic standard adopted in France. This scale
did not consider the vulnerability of buildings for es-
timating the ground shaking, and this question re-
mained for years as an important issue for interpret-
ing data collected in past macroseismic survey.

An important step in the concept of macroseismic
intensity is due to Cancani [1904]. He noticed that the
ground *"accelerations increase following a geometri-
cal rule with a common ratio of two"* as compared
with intensity. As a consequence, macroseismic in-
tensity behaves as the logarithm of the ground accel-
eration, which doubles between two degrees of in-
tensity. This makes him suggesting that the former
10-degree Rossi-Forel scale should be extended to
twelve degrees in order to cover the most devastat-
ing earthquakes [e.g. Cara et al., 2008]. Mercalli [1902]
and Sieberg [1912, 1932] followed Cancani's sugges-
tion, and introduced a detailed description of seis-
mic effects in the scale. In Europe, and in France, in
particular, the 12-degree Mercalli-Cancani-Sieberg
(MCS Scale) has been broadly used, and many suc-
cessive versions of the modified MCS are still in use
worldwide, for example, in Italy and North America,
under the name "modified Mercalli scale" [e.g., Wood
and Neuman, 1931]. In France, between 1955 and
1973, J. P. Rothé used a scale almost similar to the
MCS called EMI scale (Echelle macrosismique inter-
nationale), notably for his participation in the edi-
tion of the French building code of 1969 [Commis-
sion des règles parasismiques, 1970]; he writes in this
edition "This scale is currently the one used by al-
most all seismologists". The evolution of the MCS
scale led to the development of the MSK-64 scale
[Medvedev et al., 1964], where the characterization
of the vulnerability of buildings used in France from
1973 onwards was better described than in the mod-
ified Mercalli Scale. A first reflection on the updating
<figure><img src="image_3.png" /></figure>

O most likely vulnerability class; — probable range; ···range of less probable, exceptional cases

<caption>**Figure 1.** Differentiation of buildings structures by seismic vulnerability classes [EMS-98, Grünthal, 1998].</caption>

of the MSK-64 scale was made by the working group on macroseismic scales of European Seismological Commission at Postdam in December 1989 [Grünthal, 1989]. After discussions between the members of the European Seismological Commission, the revision of the MSK-64 gave rise to the EMS-92 [Grünthal, 1993], which was drafted in its completed form in 1998 [Grünthal, 1998] and used by BCSF from 2000 onwards. This later evolution of the scale provides us much more comprehensive view of the statistics of seismic effects used when assessing a value of intensity in a given place. Although no comparison is strictly valid between the degrees of intensity described in the different scales, Musson et al. [2010] proposed some equivalences between the previous macroseismic scale and EMS-98 in order to facilitate the reappraisal of historical earthquake data according to present standards.

The new scale better considers spatial statistics of macroseismic effects and the low vulnerability

of constructions built according to the recent earthquake-resistant building codes (Figure 1). Furthermore, EMS-98 becoming the standard in Europe, this macroseismic scale facilitates international exchange of macroseismic information across boundaries, as for the Rambervillers February 22, 2003 earthquake in the Northeast of France [magnitude 5.4, maximum intensity VI–VII; Cara et al., 2003, 2005a].

For each level of intensity, EMS-98 provides us a great deal of details in the expected behaviour of seismic indicators that can be observed and compared from place to place. Descriptions of building typologies and vulnerability classes have been detailed and expanded in this scale. Furthermore, the degrees of damage and the qualitative statements “few, many, most” are clearly defined, as summarized in Figure 2. Two full sections of the document describing the EMS-98 scale are dedicated to building vulnerability with examples. The EMS-98 is also commented with many remarks in order to help the experts in their analysis: use of negative information, uses of high buildings effects, warning on soil conditions, assessment of quality and uncertainties of intensities, and effects on the natural environment, which are mentioned but not taken into account for assessing intensity values. [EMS-98; Grünthal, 1998].

### 3. Collecting and analysing macroseismic observations

Since the establishment of the first intensity scales, macroseismic observations have been processed according to similar procedures. Observations that are comparable from one place to another (human perceptions, objects, buildings, and the natural environment) are collected through questionnaires filled by territorial authorities or during expert field surveys. More recently, spontaneous witnesses filling up Internet questionnaires provides us many observations. Observed effects displayed by the media are also considered. In a second step, macroseismic intensities are determined on the basis of an analysis of these observations according to a macroseismic scale. At the end, cartographic representation of the intensities and drawing of isoseismic lines allow us to visualize the geographical distribution of the macroseismic intensities.
<table><caption>TABLE SUMMARIZING THE DESCRIPTION OF THE DAMAGE ACCORDING TO EMS-98</caption><thead><tr><th>INTENSITIES EMS-98</th><th>V<br>(Strong)</th><th>VI<br>(Slightly damaging)</th><th>VII (Damaging)</th><th>VIII (Heavily damaging)</th><th>IX (Destructive)</th><th>X (Very destructive)</th><th>XI (Devastating)</th><th>XII (Completely devastating)</th></tr></thead><tbody><tr><th>Level of damage</th><td>D1</td><td>D1 D2</td><td>D1</td><td>D2 D3 D4</td><td>D2</td><td>D3 D4 D5</td><td>D2</td><td>D3 D4 D5</td><td>D2 D3 D4 D5</td></tr><tr><th>A (vulnerability)</th><td>F</td><td>Ma F</td><td></td><td>Ma F</td><td></td><td>Ma</td><td></td><td>Mo</td><td></td></tr><tr><th>B (vulnerability)</th><td>F</td><td>Ma F</td><td>Ma F</td><td></td><td>Ma F</td><td></td><td>Ma F</td><td></td><td>Mo</td><td></td></tr><tr><th>C (vulnerability)</th><td>F</td><td></td><td>F</td><td>Ma F</td><td></td><td>Ma F</td><td></td><td>Ma F</td><td>Mo Ma</td><td>Mo</td></tr><tr><th>D (vulnerability)</th><td></td><td>F</td><td></td><td>F</td><td></td><td>Ma F</td><td></td><td>Ma F</td><td>Ma F</td><td>Mo</td></tr><tr><th>E (vulnerability)</th><td></td><td></td><td></td><td></td><td>F</td><td></td><td>Ma F</td><td></td><td>Ma F</td><td>Mo</td></tr><tr><th>F (vulnerability)</th><td></td><td></td><td></td><td></td><td></td><td>F</td><td></td><td>Ma F</td><td>Mo</td><td>Mo</td></tr></tbody></table>

<table><tr><td>F = Few</td><td>D1* = Damage grade 1</td></tr><tr><td>Ma = Many</td><td>D2 = Damage grade 2</td></tr><tr><td>Mo = Most</td><td>D3 = Damage grade 3</td></tr><tr><td>All = All</td><td>D4 = Damage grade 4</td></tr><tr><td></td><td>D5 = Damage grade 5</td></tr></table>

<figure><img src="image_4.png" /><figcaption>Definition of quantity by EMS-98 (p.17)</figcaption></figure>

<figure><img src="image_5.png" /></figure>

C. Sira - According to
European macroseismic
scale 1998 - Grunthal & al.

<caption>**Figure 2.** Statistical table of damage grade by seismic vulnerability classes according to EMS-98.</caption>

## 3.1. *Collecting information questionnaires*

### 3.1.1. *Evolution of macroseismic questionnaires*

The structure of questionnaires has largely evolved since 1910 [Table 1, Sira et al., 2021a], from a semi-directive one (e.g., what effects did you notice?), to a list of standardized questions allowing the analyst to qualify and quantify an effect with maximum objectivity (e.g., qualification of the terms “low, medium, high” and quantification by “few, many, most”).

In the 1910 BCM questionnaire (Figure 3), the witness had to fix the Rossi-Forel intensity degree he experienced in his territorial unit by himself, according to a description of the scale given in the form. The questionnaire is presented in two parts, one for assessing intensity of the ground motion and the other one for the so-called “accidental noise” estimated with the Davison scale [Rothé, 1934]. In 1914, the sound perception scale was removed from the form, but the more general issue of acoustic noise was kept.

In 1920, the BCM questionnaire was changed (Figure 4). The Mercalli intensity with 12 degrees (Mercalli scale modified by Cancani in 1904 with 2 extra degrees at the top of the scale—according to the questionnaire in BCSF collection) can still be selected, but the witness is invited to answer additional questions, the BCSF adopted this form from 1921 to 1927.

In 1928, BCSF created its own form with a denser questioning (Figure 5). However, the effects of several indicators (buildings, crockery, furniture, objects, or

chimneys, etc.) are sometimes grouped together in a single question. The semi-directive questionnaire mentioned a single type of effect only (example: vibration of crockery). This leads to uncertainty and the impossibility of discretizing the effects according to different levels, as is done with a modern form (weak, medium, strong vibration, displacement, falling objects). The proportion of people who felt the earthquake, for example, is formulated in its simplest description: “did more than one person felt the earthquake in the locality?”

BCSF used this form until 1978 [Sira et al., 2021a], while the macroseismic scales in use (MCS, EMI, MSK-64) were evolving towards an increasingly fine gradation of effects and indicators. It is therefore likely that the 1928 questionnaire leads to an increasing uncertainty in the reported macroseismic intensity over time, until a questionnaire more adapted to the scale in use is introduced.

In 1978, a new questionnaire based on the MSK-64 scale was designed by BRGM. The witness is no longer invited to determine the intensity by himself, but he must fill in a check boxes questionnaire. Questions are sorted according to observation types, and typical effects are given (vibration of dishes, falling objects, etc.). For the first time, the percentage of these effects (5%, 50%, 75%) is asked at the communal level. Damage to buildings by degree and frequency associated with the three MSK-64 vulnerability classes are requested. It is clear that this new scale, and the associated questionnaire have a major impact on the quality and accuracy on the
<figure><img src="image_6.png" /><figcaption>**Figure 3.** 1910 questionnaire of the Bureau central météorologique français based on the Rossi-Forel and Davison scales (BCSF archives).</figcaption></figure>

estimated intensities. The intensity degree has then been determined by the expert analyst and no longer by the person answering the questionnaire [Schlich, 1984].

Slight changes were made when BCSF took back the surveys in 1986. Acoustic noise, often mentioned by witnesses but absent in the MSK-64 scale, has been reintroduced. A revision of the questionnaire was made in 1995 with a few additional questions. This later change could have improved the quality of the information collected, but it made the questionnaire more difficult and longer to fill.

In 2000, BCSF adopted the EMS-98 scale. Two questionnaires were then designed, one dedicated to city agents asking for the effects observed over the whole commune, hereafter referred to “communal” questionnaire, and one dedicated to isolated witness, hereafter referred to “individual” questionnaire. Except for the number of classes of vulnerability of the constructions considered, the change in the list of questions between the MSK-64 and EMS-98

questionnaires remain marginal. Its layout was adapted to semi-automatic optical recognition.

In 2004, after experiencing the survey of the 2003 Rambervillers earthquake, the communal questionnaire was improved in order to better assess the percentages by type of structure (stone, concrete, wood, etc.), as well as the number of damages observed in each category. A version of the questionnaire adapted to the types of constructions of the West Indies was designed after the earthquake in Guadeloupe on November 21, 2004.

In 2001, the first French online individual questionnaire “j’ai ressenti le séisme” was launched by BCSF (Figure 6). It was completed in 2004 by adding seven thumbnails describing the felt effects for the degrees II to VIII of EMS-98 (Figure 7). The idea was then to cross-check the coherency between answers to the questionnaire and the more global view coming from the selected thumbnails [Sira, 2018]. This is, to our knowledge, the first time that such a strategy was implemented worldwide.
Monsieur, vous-êtes prié de bien vouloir remplir le présent Questionnaire et le renvoyer à la Station Centrale sismologique, 9, rue Herder, Strasbourg.

Questionnaire.

Tremblement de terre (1)

samedi 28 septembre (nuit du 22 au 23)

Localité Anglés

Heure

<figure><img src="image_7.png" /></figure>

1 h.

m.

s.

(3)

Avant midi ou après midi?

Où était l'observateur ?

En plein air ?

Dans une maison ?

oui

A quel étage ?

<figure><img src="image_8.png" /></figure>

Nombre, durée des secousses? (3)

<figure><img src="image_9.png" /></figure>

Direction des secousses? (4)

<figure><img src="image_10.png" /></figure>

Intensité? (5)

<figure><img src="image_11.png" /></figure>

Effets du tremblement de terre

<figure><img src="image_12.png" /></figure>

Bruits sismiques?

<figure><img src="image_13.png" /></figure>

Etat des sources, des fontaines?

Autres observations:

Adresse de l'observateur :

<figure><img src="image_14.png" /></figure>

Échelle des Intensités.

1er Degré: Mouvement microsismique, noté par les sismographes seulement.

2e * : Secousse enregistrée par les sismographes et constatée seulement par un petit nombre d'observateurs au repos.

3e * : Ebranlement constaté par plusieurs personnes au repos; assez fort pour que la durée ou la direction puissent être appréciées.

4e * : Ebranlement constaté par des personnes en activité, faiblement en plein air, mieux dans les maisons, ébranlement des objets mobiles, des portes, des fenêtres, craquement des planchers.

5e * : Ebranlement constaté en général par toute la population; ébranlement d'objets plus lourds; de meubles et de lits; tintement de quelques sonnettes.

6e * : Réveil général des dormeurs; tintement général des sonnettes, oscillation des lustres, arrêt des pendules; ébranlement apparent des arbres. Des personnes effrayées sortent des habitations.

7e * : Renversement d'objets mobiles; chute des plátras du plafond et des murs; tintement des cloches dans les églises; épouvante générale sans dommage aux édifices bien construits.

8e * : Chute des cheminées; lézardes dans les murs.

9e * : Destruction partielle ou totale de quelques édifices.

10e * : Des bâtiments très solides sont détruits. Il se produit des fentes dans le sol. — L'eau des rivières, lacs, etc. est projetée.

11e * : Catastrophe. — Destruction des bâtiments, ponts, digues. — Rails tordus, débordement des eaux.

12e * : Grande catastrophe. — Aucune œuvre ne subsiste, montagnes effondrées, ébranlées. — Des chutes d'eau se forment etc.

<caption>**Figure 4.** 1920 questionnaire based on the 12-degrees Mercalli scale (BCSF archives).</caption>

<footnote>(1) Jour de la semaine et date.</footnote>

<footnote>(2) Heure moyenne locale (heure du fuseau) ou Heure légale.</footnote>

<footnote>(3) Remplir autant de questionnaires semblables qu'il y a eu de secousses distinctes.</footnote>

<footnote>(4) Par exemple: Est-Ouest, chc de bas en haut.</footnote>

<footnote>(5) L'intensité se marque par un N°. Consulter l'échelle des Intensités ci-jointe.</footnote>
<figure><img src="image_15.png" /><figcaption>**Figure 5.** 1928 questionnaire based on the 12-degrees Mercalli modified scale (BCSF archives).</figcaption></figure>

The most recent change in the communal questionnaire was made in 2009 in order to better describe the damage in buildings. Today, several information on residential building categories are accessible in public databases for French localities. Land declaration database, such as MAJIC II [Martin et al., 2008], allows us to estimate a vulnerability profile at the scale of a city or district [Schlupp et al., 2011]. Future versions of the questionnaire could be simplified and developed in a conditional questionnaire (some questions only appear when they become relevant) making the questionnaires shorter and more pertinent to the person filling out the questionnaire.

### 3.1.2. Collection of data with questionnaires

In France, systematic macroseismic investigation by a central service started at BCM after the Lambesc earthquake of June 11, 1909. Following this event, 4200 questionnaires were returned, filled in by the

mayors and teachers of all concerned communes [Angot and Lemoine, 1910, Fréchet, 2008]. After 1921, Edmond Rothé, director of BCSF, pursued the way BCM organized the dissemination of questionnaires. For example, after the Rastatt, Germany, earthquake of February 8, 1933, among 1500 questionnaires sent, 1329 were returned, allowing BCSF to determine 530 intensity data point (IDP) [Rothé, 1934]. IDP determines the geographical location, the name of the place (usually the commune), and the intensity value in a given macroseismic scale.

The local press, which is rich in reports of data corresponding with small intensities, may bear valuable additional information, but it is used by BCSF only in rare circumstances [Vogt, 2003]. Calls for testimonials have sometimes been relayed in daily newspapers such as in "France Soir" when Professor Lemoine from the "Musée d'Histoire Naturelle" insert a macroseismic questionnaire after the Flanders earthquakes of June 1938 [Rothé, 1941].
Formulaire d'enquête

du Bureau Central Sismologique Français

Temps nécessaire pour remplir le questionnaire : 3 minutes.

<figure><img src="image_16.png" /><figcaption>**Figure 6.** Extract from the first BCSF online internet questionnaire in 2001.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>**Figure 7.** Extract of thumbnails to be selected in BCSF individual macroseismic questionnaire based on EMS-98 (inside building part).</figcaption></figure>
<table><caption>**Table 1.** Summary table of macroseismic questionnaires from BCSF archives</caption><thead><tr><th rowspan="2">Macroseismic Investigation Agency</th><th rowspan="2">BCMF</th><th rowspan="2">Imperial main station for earthquake research in Strasbourg (Kaiserliche Haupstätte für Erbebenforschung in Strasbourg)</th><th rowspan="2">IPGS</th><th colspan="3">100 YEARS OF BCSF</th></tr><tr><th>BCSF</th><th>BRGM</th></tr></thead><tbody><tr><td>Period of use</td><td>1909(7)-1919</td><td>1900(7) to 1918(7)</td><td>1920 to 1921</td><td>1921 to 07/1927</td><td>07-1927/1977</td><td>11/1978 to 04/1986</td></tr><tr><td>Quetsonnaire</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(1) Date of creation of the form used</td><td>1909 (7)</td><td>1900(7)</td><td>1920</td><td>1920</td><td>07-1927</td><td>11-1978</td></tr><tr><td>(2) Version of form</td><td>V. 0a</td><td>V. 0b</td><td>V.1</td><td>V.1</td><td>V.2</td><td>V.3</td></tr><tr><td>(3) Media</td><td>paper</td><td>paper</td><td>paper</td><td>paper</td><td>paper</td><td>paper</td></tr><tr><td>(4) Macroseismic Scale used</td><td>Rossi-Forel</td><td>(7)</td><td>MCS</td><td>MCS</td><td>MCS (1927-1955), TMI (1955-1973), MSK64 (1973-1977)?</td><td>MSK64</td></tr><tr><td>(5) Spatial extent of the questionnaire (to the address and/or the municipality)</td><td>individual + communal</td><td>individual</td><td>individual + communal</td><td>individual + communal</td><td>communal</td><td>communal</td></tr><tr><td>(6) Witness location (city, street)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(7) Witness location (floor)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(8) Questions format: open-ended</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(9) Questions format: semi-structured</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(10) Questions format: structured</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(11) Number of questions</td><td>8</td><td>12</td><td>16</td><td>16</td><td>13</td><td>12</td></tr><tr><td>(12) Affected neighbouring localities</td><td></td><td></td><td></td><td></td><td>yes</td><td>yes</td></tr><tr><td>(13) Effects on people</td><td>no</td><td>yes</td><td>no</td><td>no</td><td>yes</td><td>yes</td></tr><tr><td>(14) Quantification of effects on people</td><td></td><td></td><td></td><td></td><td>yes (1 level)</td><td>yes (3 levels)</td></tr><tr><td>(15) Effects on animals</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(16) Direction of the shaking</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(17) Effects on objects</td><td>semi-structured question* (effects produced?)</td><td>semi-structured question (effects produced?)</td><td>semi-structured question (effects of the earthquake?)</td><td>semi-structured question (effects of the earthquake?)</td><td>semi-structured question (effects produced?)</td><td>yes</td></tr><tr><td>(18) Quantification of effects on objects</td><td></td><td></td><td></td><td></td><td></td><td>yes</td></tr><tr><td>(19) Environmental information</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(20) Geological Subsurface Information</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(21) Noises heard</td><td>yes (Davison scale)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(22) Number, duration of shaking</td><td>yes</td><td>yes (just number)</td><td>yes</td><td>yes</td><td>yes</td><td>yes (just number)</td></tr><tr><td>(23) Effects on springs, fountains, wells</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(24) Wind direction and strength</td><td>yes</td><td>yes</td><td></td><td></td><td></td><td></td></tr><tr><td>(25) State of the sky at the time of the earthquake</td><td>yes</td><td>yes</td><td></td><td></td><td></td><td></td></tr><tr><td>(26) Effects on constructions</td><td>semi-structured question (effects produced?)</td><td>semi-structured question (effects produced?)</td><td>semi-structured question (effects produced?)</td><td>semi-structured question (effects produced?)</td><td>semi-structured question (effects produced?)</td><td>yes</td></tr><tr><td>(27) Type of damage (number of question)</td><td></td><td></td><td></td><td></td><td>semi-structured question (type of damage)</td><td>yes (10)</td></tr><tr><td>(28) Vulnerability of affected structures (number of vulnerability classes)</td><td></td><td></td><td></td><td></td><td></td><td>yes (3)</td></tr><tr><td>(29) Vulnerability profile of the municipality (number of vulnerability classes)</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(30) Quantification of the effects on constructions (number of levels)</td><td></td><td></td><td></td><td></td><td></td><td>yes (Rare, Many, Generalized)</td></tr><tr><td>Analysis</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(31) Selection of the degree of intensity from a scale description</td><td>yes</td><td></td><td>yes</td><td>yes</td><td>yes</td><td></td></tr><tr><td>(32) Selection of the degree of shaking from thumbnails</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(33) intensity given by the witness (from scale description)</td><td>yes</td><td></td><td>yes</td><td>yes</td><td>yes</td><td></td></tr><tr><td>(34) Estimation of intensity by question fields</td><td>yes</td><td></td><td>yes</td><td>yes</td><td>yes</td><td></td></tr><tr><td>(35) Communal SQL average of thumbnails</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(36) Calculation of epicentral intensity</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(37) Indication of maximum intensity</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Cartography</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(38) Plotting of the isoiseis</td><td>manual</td><td></td><td>manual</td><td>manual</td><td>manual</td><td>manual</td></tr><tr><td>(39) Plotting of iso-acoustics</td><td></td><td></td><td></td><td></td><td>1933</td><td></td></tr><tr><td>(40) Mapping of effects on indicators (object, feelings, noise)</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(41) Rapid and preliminary mapping of intensities</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(42) Color maps used</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(43) Integration of macroseismic data in shakemap</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Archive</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>(44) Data archive</td><td>paper</td><td></td><td>paper</td><td>paper</td><td>paper</td><td>paper</td></tr><tr><td>(45) Publication</td><td>Annales du BCSF</td><td>Annales du BCSF</td><td>Annales de l'Institut de Physique du Globe</td><td>Annaude de l'Institut de Physique du Globe / Observations simologiques du BCSF</td><td>Observations simologiques du BCSF</td><td></td></tr></tbody></table>

semi-structured question: These questions allow a free response on an abroad topic, or focus on one aspect of the topic.
number in brackets (1): number of questions concerned

(continued on next page)
<table><caption>**Table 1. (continued)**</caption><thead><tr><th colspan="11">100 YEARS OF BCSF</th></tr><tr><th colspan="11">BCSF</th></tr><tr><th>Macrostructural Investigation Aspect</th><th>1986/07 to 1996/07</th><th>1996/07 to 1999/12</th><th>01/2000 to 12/2003</th><th>01/2000 to 05/2004</th><th>01/2004 to 12/2008</th><th>06/2004 to 2021</th><th>04/2010 to 02/2016</th><th>01/2009 to 2021</th><th>11/2019 to 2021</th></tr></thead><tbody><tr><td>(1)</td><td>07-1986</td><td>1996</td><td>2000</td><td>2000</td><td>2004</td><td>06/2004</td><td>04/2010</td><td>2009</td><td>11/2019</td></tr><tr><td>(2)</td><td>V.4</td><td>V.5</td><td>V.6</td><td>V.7 (a&b)</td><td>V.8</td><td>V.9 (a&b)</td><td>V9C</td><td>V.10 (a&b)</td><td>V.11</td></tr><tr><td>(3)</td><td>paper</td><td>paper</td><td>paper</td><td>paper / online (since 2002)</td><td>paper</td><td>paper (PDF)/online</td><td>smartphone application (IOS system)</td><td>paper (PDF)/online</td><td>paper (PDF)</td></tr><tr><td>(4)</td><td>MSK64</td><td>MSK64</td><td>EM598</td><td>EM598</td><td>EM598</td><td>EM598</td><td>EM598</td><td>EM598</td><td>EM598</td></tr><tr><td>(5)</td><td>communal</td><td>communal</td><td>communal</td><td>individual</td><td>communal</td><td>individual</td><td>individual</td><td>communal</td><td>individual damages</td></tr><tr><td>(6)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(7)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(8)</td><td>yes</td><td>yes</td><td>yes</td><td>yes [1]</td><td>yes [1]</td><td>yes [1]</td><td>yes [1]</td><td>yes [1]</td><td>yes [1]</td></tr><tr><td>(9)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(10)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(11)</td><td>29</td><td>50</td><td>53</td><td>51</td><td>47</td><td>51</td><td>6</td><td>49</td><td>7</td></tr><tr><td>(12)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(13)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(14)</td><td>yes</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td><td>yes [3 levels]</td></tr><tr><td>(15)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(16)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(17)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(18)</td><td>yes</td><td>yes</td><td>yes</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td></tr><tr><td>(19)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(20)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(21)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(22)</td><td>yes (another tremor?)</td><td>yes (another tremor?)</td><td>yes (another tremor?)</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td></tr><tr><td>(23)</td><td>yes</td><td>yes</td><td>yes</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td><td>yes [1 semi-structured question]</td></tr><tr><td>(24)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(25)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(26)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(27)</td><td>yes (9)</td><td>yes (14)</td><td>yes (17)</td><td>yes (17)</td><td>yes (12)</td><td>yes (17)</td><td>yes (14)</td><td>yes (5)</td><td>yes (5)</td></tr><tr><td>(28)</td><td>yes (3)</td><td>yes (3)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td></tr><tr><td>(29)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td><td>yes (6)</td></tr><tr><td>(30)</td><td>yes (f flare, Many, Generalized)</td><td>yes (Few &amp; Very much)</td><td>yes (Few &amp; Very much)</td><td>yes (2)</td><td>yes (3) + exact number</td><td>yes (2)</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(31)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(32)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(33)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(34)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes (2004 - 2018)</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(35)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(36)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(37)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(38)</td><td>manual</td><td>manual</td><td>numerical interpolation by IDW-manual</td><td>numerical interpolation by IDW-manual</td><td>numerical interpolation by IDW-manual</td><td>numerical interpolation by IDW-manual or Kriging (2014)</td><td>numerical interpolation by IDW-manual or Kriging (2014)</td><td>numerical interpolation by IDW-manual or Kriging (2014)</td><td>numerical interpolation by IDW-manual or Kriging (2014)</td></tr><tr><td>(39)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(40)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(41)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(42)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(43)</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td><td>yes</td></tr><tr><td>(44)</td><td>database</td><td>database</td><td>database</td><td>database</td><td>database</td><td>database</td><td>database</td><td>database</td><td>database</td></tr><tr><td>(45)</td><td>Observations sismologiques du BCSF</td><td>Observations sismologiques du BCSF</td><td>Observations sismologiques du BCSF/Technicals reports</td><td>Observations sismologiques du BCSF/Technicals reports</td><td>Observations sismologiques du BCSF/Technicals reports</td><td>Observations sismologiques du BCSF/Technicals reports</td><td>database/Technicals reports</td><td>database/Technicals reports</td><td>Technicals reports</td></tr></tbody></table>
In 1940, during the Second World War, BCSF moved to Clermont-Ferrand, South of the armistice line of demarcation. BCSF macroseismic investigations were made possible until 1950, thanks to the press media and the staff of the French meteorological stations [Rothé, 1941, 1954]. Reports from the observers of meteorological stations remain an important source of information until 1961.

After the large earthquake in Arette of August 13, 1967 in the Pyrenees, 1191 questionnaires were sent back to BCSF (Figure 8) while, on its own initiative, the geography department of Pau launches an ad hoc macroseismic questionnaire and gathers more than 1500 answers from school teachers. Many such studies conducted by individuals, on their own initiative, were reported to BCSF. This is the case of the seismologist Pierre Stahl for the south west of France. If the observations collected induce some uncertainty in the estimated intensity, Pierre Stahl's network of observers allows us to determine intensities for very low magnitude events, rarely surveyed by BCSF.

At the end of the 1970s, seismic alerts launched 24 hours a day by the geophysical laboratory of the French "Commissariat à l'Energie Atomique" (CEA), in close connection with the Civil Security authorities, became the main source of information for starting macroseismic investigations, in particular for low-magnitude events, solely locally felt. The more or less lack of interest in macroseismic surveys by academic organizations, the need to better take into account seismic hazard in the growing French nuclear plant programme, and the retirement of Jean-Pierre Rothé in 1975, motivated BRGM to take over the conduct of the surveys in 1978. "BRGM has recreated a network of correspondents with the Civil Security authorities. Public awareness and support of the regional press have greatly facilitated the work of the investigators" according to Vogt [2003].

After 1980, the development of the academic instrumental network "Réseau national de surveillance sismique—Rénass" with headquarters located next to BCSF in Strasbourg became the new actor complementing the CEA network for launching macroseismic investigations. After nine years of macroseismic investigation based on the MSK-64 scale, BRGM reduced its involvement in this field and the management of the surveys came back to BCSF pursuing the survey model used by BRGM.

Until 2000, the distribution of communal paper questionnaires, with the help of the regional authorities, was the rule. After having tested several types of distribution networks, it became obvious that the development of the Internet could deeply change the way to collect macroseismic information. The first opportunity for BCSF to test such an Internet procedure was the 2003 Rambervillers earthquake [Cara et al., 2003]. BCSF collected nearly 13,000 individual Internet testimonies and 7376 communal questionnaires. Thanks to the new Internet media, 6154 IDP have then been obtained at distances up to about 650 km away from the epicentre (Figure 9).

In early 2009, the communal paper questionnaire procedure was replaced by an Internet communal questionnaire dedicated to local authorities through restricted access. The answers are then directly integrated into a database for analysis. This reduced the delay time for launching macroseismic investigation to less than 48 hours after the earthquake. In February 2010, BCSF launched the first smartphone application SismoCom in order to collect individual testimonies based on a selection of thumbnail images (Figure 7) [Sira et al., 2010]. Stopped in 2016, this application will be replaced by an adaptive multi-platform system.

In the French West Indies, since Les Saintes Earthquake in 2004 [Cara et al., 2005b], the "Observatoire sismologique et volcanologique de Guadeloupe" and the "Observatoire sismologique et volcanologique de Martinique" of "Institut de Physique du Globe de Paris" systematically relays the calls for individual testimonies, as well as for communal surveys requested by the governmental regional authorities.

In Mayotte, Indian Ocean, REVOSIMA (Réseau de surveillance volcanologique et sismologique de Mayotte), created after the volcano-seismic crisis that started in June 2018, now helps to relay the calls for individual testimonies. BCSF was set up in 2020 with a group of correspondents with the Mahoran authorities in order to respond online to communal questionnaires after significant earthquakes.

Since 2000, in order to increase the number of individual testimonies for each macroseismic survey, a BCSF press release is sent directly to the regional and/or national media. It was replaced in 2014 by an automatic seismological information mailing list. In 2009, two social pages were created on Twitter (@franceseisme, 4955 followers in 2020)
<figure><img src="image_18.png" /></figure>

**Figure 8.** Evolution of macroseismic map, Arette earthquake 1967 [Rothé, 1972], La Rochelle earthquake isoseists drawing by kriging interpolation [Sira et al., 2016a].

<figure><img src="image_19.png" /></figure>

**Figure 9.** Cross-border macroseismic intensity map of the Rambervillers earthquake, February 2003, ML 5.4 [Cara et al., 2003].
and Facebook (@franceseisme, 4460 subscribers) for the same purpose. Today, BCSF launches around twenty macroseismic surveys per year in metropolitan France and the overseas territories.

### 3.1.3. Collection of data by field survey

Field survey conducted by experts is the only way to reliably estimate macroseismic intensities in localities, where the level of shaking causes damage on the most vulnerable constructions ($I \ge V$). Indeed, the vulnerability of buildings and the frequency of damage are then key information for a correct evaluation of intensity. During the XXth century, macroseismic field surveys have been very limited in France. Among noticeable exceptions, let us mention commandant Spiess' survey. As a military officer and member of the French Geological Society, he reported damage assessment after the 1909 Provence earthquake with rigour and accurate details [Lambert, 1997], and Rothé and Vitart [1969] reported their survey of the 1967 Arette earthquake in the Pyrenees with description of the damage in relation to the building vulnerability.

A first inter-agency collaboration in the field was launched in 2003, after the Rambervillers earthquake. Four scientists were involved [Cara et al., 2003] for estimating 35 communal intensities. In 2004, the November 21st Saintes earthquake in Guadeloupe, French West Indies, (magnitude 6.4, maximal intensity VII–VIII EMS-98) was the occasion of renewing this collaboration in the field. It made it possible to estimate 32 communal intensities [Cara et al., 2005a]. In 2007, 11 scientists took part in the macroseismic study in Martinique after the November 29th earthquake (magnitude 7.4, $I_{max}$ VI–VII EMS-98) and 34 communal intensities were determined [Schlupp et al., 2008]. The necessity for launching a field survey above intensities V motivated BCSF to create the French macroseismic intervention group (Groupe d'intervention macroseismique (GIM)) in 2011 [Sira, 2015].

In 2011, in connection with the GIM, BCSF brought together 18 new members for a first training session dedicated to field investigations, in particular for vulnerability and damage degree assessment according to EMS-98 scale. Specific documents for estimating the degree of vulnerability and damage have been prepared and are regularly improved after each field surveys. To date, BCSF has organized

8 training sessions for more than 80 experts from France and neighbouring countries ready to participate in macroseismic field surveys.

The GIM was activated after the 2014 Barcelonnette earthquake in the Alps, [Sira et al., 2014], the 2016 La Rochelle earthquake on the west coast of metropolitan France [Sira et al., 2016a], the volcanic crisis in Mayotte [Sira et al., 2018] and the November 11, 2019 Le Teil earthquake in the Rhone valley ($I_{max}$ = VII–VIII) [Schlupp et al., 2021]. The GIM field surveys have to take place in the days following the earthquake, after the rescue of the victims and before, when possible, a series of aftershocks which could make it difficult assessing the intensities of the main shock. Based on his experience with the GIM, BCSF participates in a joint effort to set up a cross-border macroseismic group trained with experts from France, Spain, and Andorra (GIM-PYR) dedicated to field survey of potential damaging earthquakes in the Pyrenees (POCRISC.eu, For a Common Culture of Seismic Risk).

### 3.2. Analysis of macroseismic information

Little information is available on the analytical methods used at BCSF for estimating intensities, other than to rely on descriptions of macroseismic scales. Unfortunately, the scale used is not systematically indicated on published macroseismic assessments, and only the search for clues in publications or on the questionnaires themselves can confirm this with more or less certainty. Although some variations in the interpretation of questionnaires occur from one expert to another with the same scale; the most recent scales reduce this difference and open up the reinterpretation of past questionnaires once a clear and shared decision strategy has been decided upon.

The 1928 questionnaire, used by BCSF until 1978, invites the witnesses to give some various information, including their own assessment of macroseismic intensity. In the light of this questionnaire, it is clear that in case of building damage, little attention is paid to the vulnerability classes and the frequency of damage. Without information coming from additional sources, reassessing intensities from the questionnaires is almost impossible according to modern standards. Except in a few cases, the reassessed intensity values should thus present a large uncertainty. Such an exception is the February 10, 1937
earthquake in Algeria (I<sub>max</sub> = IX), for which a particu-
lar attention was, for example, paid to the description
of damage [Rothé, 1940].

Another issue that often arose from the use of
the ancient scales is the presence of intermediate
value between two intensity values. These intermedi-
ate values (e.g., V–VI) do not necessarily represent the
same information and unfortunately, no information
is given in the publication about the exact signifi-
cance of these intermediate values. Sometimes they
express uncertainty in the intensity values, some-
times they result from the average of communal val-
ues over a larger territorial unit such as the “canton”
as it is the case for the earthquake of the June 11,
1938, in Belgium [Rothé, 1941]. Half values of inten-
sity may also reflect the presence of two distinct val-
ues within the site under study, as it is sometimes
the case for intensity determined during more pre-
cise field surveys since 2000 [Les Saintes earthquake,
2004; Barcelonnette earthquake 2014; Le Teil earth-
quake, 2019 [Schlupp et al., 2021]].

Vogt [2003] pointed out that in the past, many of
the BCSF intensity estimates are questionable. To the
credit of the analysts in charge of the intensity deter-
minations at BCSF, the shortcomings in the qualifi-
cation and quantification of the effects in the 1928
BCSF questionnaire could only leave a large part of
subjectivity in the evaluation or re-evaluation of in-
tensities. This is only since 1978 that the BRGM ques-
tionnaire became formatted as a series of questions,
facilitating the determination of intensity by experts.
The fact that different macroseismic scales are re-
ferred to in BCSF data base (12-degrees Mercalli,
MSK-64, and now EMS-98) is an additional difficulty
for assessing homogeneous macroseismic intensi-
ties in earthquake catalogues. In order to circumvent
these difficulties, the historical database SisFrance
uses a unique macroseismic scale (MSK-64) when re-
assessing the different intensities, while BCSF keeps
the original values in its database, leaving the user
making the choice of conversion table to interpret the
different values.

For the February 29th, 1980 Arudy earthquake in
the Pyrenees, the building damage degrees and vul-
nerabilities have been reported and considered ac-
cording to MSK-64. However, even in this case, the
vulnerability information remains too poor for deter-
mining the proportion of damages per class of vul-
nerability for both MSK-64 and EMS-98 intensity es-

timations. Since 2000 and the use of EMS-98, the
analysis of the building information is improved. The
knowledge of the vulnerability classes at the commu-
nal level [Schlupp et al., 2011] helps us to better es-
timate the frequency of damage degree by class of
vulnerability and then greatly improves the quality
of the intensity value as representative of the ground
shaking.

Since 2000, communal intensities are determined
at BCSF following two main methods. First, within
a commune, a preliminary intensity is rapidly esti-
mated from individual testimonies and the thumb-
nails selected by witnesses. In the case of a few obser-
vation points, no statistic on indicators effects can be
done within the commune, and the selected thumb-
nails method just provides us a Single Questionnaire
Intensity (SQI) for each geolocated individual testi-
monies (city, street, or exact address). Testimonies at
floors above the 4th or underground are excluded,
and SQI at 3rd and 4th floors are reduced by 1 de-
gree. The automatic average of SQIs per municipality
gives us a preliminary intensity for rapid information
[Sira et al., 2016b]. From 2004 to 2016, 35,000 ques-
tionnaires were analysed by hand in order to com-
pare the individual intensities so obtained with the
values of individual intensity coming from the se-
lected thumbnails [Sira et al., 2013]. In these prelimi-
nary intensities, an underestimation of epicentral in-
tensities higher than V was noted, mainly due to the
absence of testimonies from people who were heavily
affected by the damage and were mainly busy solv-
ing accommodation, insurance, and security prob-
lems [Sira et al., 2021a,b, Schlupp et al., 2021].

Second, the communal reference intensity is de-
termined from the answers to the EMS-98 commu-
nal questionnaires. If there are more than 10 SQIs col-
lected in the same commune, the answers to individ-
ual questionnaires are also considered in the anal-
ysis. In the case of an earthquake generating dam-
age to buildings, the GIM group carries out in the
field an assessment of degree of damage (5 levels)
for each vulnerability class (6 classes) and their fre-
quency in each commune. These results are then
compared with the statistical levels expected in the
EMS-98 scale for each intensity (Figure 10) in or-
der to determine the definitive intensity. Additional
data provided by the communal authorities can com-
plete the set of documents used in this evaluation.
Let us note that the statistical representation of the
<figure><img src="image_20.png" /><figcaption>**Figure 10.** Damage comparison tool with EMS-98 descriptions by intensity levels, e.g., by average statistics approach (the statistical reference level (base of calculation) can be changed in this comparison file).</figcaption></figure>

macroseismic observations collected by the authorities can be affected by some biases, but the definition in EMS-98 of the quantity within three levels (few, many, at most) limits its impacts on the quality of the intensity estimation and at the end, the GIM estimates are predominant over all other analyses.

### 3.3. Mapping representation

Macroseismic intensities of the most significant earthquakes are presented on isoseism maps since the Neopolitan earthquake in 1857 [Oliveira, 2021]. These types of maps have undergone a strong evolution due to the plotting method as well as ways of representing the intensities (Figure 8). In addition to intensities, local directionality or site effects correlated with the geology are sometimes shown on the map [Rothé, 1941]. BCSF published the first map of isoseists for three earthquakes in the Pyrenees in 1922 [Rothé, 1923]. In the past, many isoseismal maps were described in BCSF reports but were not printed [Rothé, 1924]; the high cost of reproducing such maps in publications prevented their publication [Rothé, 1924]. With a few exceptions,

mainly tables of intensity were reported until 1935. BCSF archive contains many unpublished manual drawings of intensity maps. The number of macroseismic maps increased rapidly when Jean-Pierre Rothé became director of BCSF [Rothé, 1954].

The colour maps, together with the first numerical drawing of isoseists were produced for the 1989 events [Schlich and Hoang Trong, 1994], while previously, they were drawn by hand by an expert. In 2000, the Geographic Information System (GIS) allowed to perform a computer interpolation of intensity points and then semi-automatic isoseismic lines. The spatial distribution of intensities is based on colour ranges overlaid on topographic maps. Until 2012, the interpolation was based on a deterministic Inverse Distance Weighting (IDW) approach and since 2016 on kriging (Figure 8). Since 2012, an automatic rapid mapping of preliminary communal intensities (Figure 11) is implemented on the BCSF-Rénass website (www.franceseisme.fr) based on the average SQI of individual testimonies, as well as maps of some others indicators of seismic effects (Figure 12): noise, falling objects, and witness perception. This mapping is automatically updated as soon as new information are received.
<figure><img src="image_21.png" /><figcaption>**Figure 11.** Preliminary internet intensity map (www.franceseisme.fr, 2012), Saint-Pé-de-Bigorre (Pyrénées) earthquake (31/12/2012, ML: 4.9).</figcaption></figure>

Because many earthquakes in Europe are located near the country borders, merging coherent macroseismic information in cross-border maps is also an important issue (e.g., Figure 9 for the Rambervillers earthquake). After the recent work of Van Noten et al. [2017] aimed at merging the cross-border intensities data of the 2011 ML 4.3 Goch earthquake (SE UK), and the 2015 ML 4.2 Ramsgate (Germany), an European mapping project merging individual Internet testimonies is being developed by the Macroseismic working group of the European Seismological Commission.

### 3.4. *Storage and dissemination of information*

Since 1921, BCSF archives have been mainly managed by the “Institut de Physique du Globe de Strasbourg” (now by EOST) within the Faculty of Sciences of the French University of Strasbourg.

When BCSF moved to Clermont-Ferrand during the Second World War, some documents may have been lost but many original works have been preserved. BCSF archives include data on all earthquakes studied and felt in metropolitan France and overseas since 1919. Macroseismic survey documents from 1919 to 2012 are kept in a dedicated room in archival boxes on about 40 linear metres [Schirr, 2011]. Unfortunately, fungi affect some of the oldest boxes and other documents have suffered from mechanical damage. To safeguard this content of scientific value, the digitization of 70,000 selected documents, out of about 350,000, started in 2020 with the strongest earthquake documents. They contain individual data subject to the GDPR (https://ec.europa.eu/info/law/law-topic/data-protection/data-protection-eu_en), but they should be progressively accessible online for scientists from 2022.
<figure><img src="image_22.png" /><figcaption>**Figure 12.** Map of the effects on witnesses (most frequent value in the commune, all floors of the witness): panic (in red), fear (in yellow), anxiety (in green), without anxiety (in grey). Le Teil earthquake 2019 (ML 5.2).</figcaption></figure>

In 2000, BCSF developed a macroseismic database called “Epicentre” for the storage of information allowing the mapping of results with a GIS. The macroseismic questionnaires from 1996 to 2012 are stored in digital format, as well as all the estimated intensities in the different macroseismic scales since 1920. After 2012, the online questionnaires, individual and communal, have been integrated into the database.

To date, BCSF database contains more than 121,000 communal intensity data points (IPD) starting in 1921 for nearly 2000 recorded events. Since 1996, more than 181,000 questionnaires have been recorded in the database (Figures 13, 14, 15). Today, definitive IDP starting from 1996 are included in a Contemporary Macroseismic Database which are freely accessible online (http://www.franceseisme.fr//donnees/BD-MFC/). A new database is being developed with all IDP and connection between the macroseismic and instrumental

data. The SisFrance historical intensities (BRGM—Electricité de France—Institut de radioprotection et de sûreté nucléaire) will also be associated with the intensities of BCSF-Rénass.

Sixty macroseismic reports, illustrated with numerous maps, have been published on www.franceseisme.fr for the most important French earthquakes since 1989.

## 4. Use of the French macroseismic data

Despite the development of permanent seismic networks, except when dense local networks are present, as in the Alps and the Pyrenees, macroseismic data remain the only, or if not the most relevant data, in the first kilometres around the epicentres. The nearly 35,000 French municipalities indeed form a much denser network than the about 400 sites equipped
<figure><img src="image_23.png" /><figcaption>**Figure 13.** Location of macroseismic surveys in BCSF-Rénass macroseismic database.</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>**Figure 14.** Number of intensity data points in BCSF-Rénass macroseismic database.</figcaption></figure>

with seismic sensors. The only limitation is the presence of observers in the affected area who can report macroseismic observations or macroseismic indicators affected by the shaking (objects, buildings).

Far from drying up, as might have been thought at the end of the 20th century, the volume of macroseismic data collected is still increasing rapidly. Those interested in earthquakes and seismic risk fre-
<figure><img src="image_25.png" /><figcaption>**Figure 15.** Number of macroseismic surveys in BCSF-Rénass macroseismic database.</figcaption></figure>

quently consult data that are disseminated and published by BCSF-Rénass like preliminary maps produced quickly, finalized reference maps, or various analyses.

The use of macroseismic data and intensities is constantly increasing and their dissemination is largely facilitated by the implementation of databases and Application Programming Interface (API) at BCSF-Rénass. The main purposes are: behaviour of the observed indicators (people, objects, furniture, constructions), severity of the tremor, estimation of the affected zone, calibration of source and attenuation parameters in relation to instrumental data, ground motion modelling, site effects, risk management, scenario simulation, seismic hazard assessment; so many fields in which macroseismic data are today indispensables.

## 4.1. Earthquake parameters

At the territorial level, instrumental catalogues, mainly for events after the 1960s [Cara et al., 2015], display accurate epicentre locations, but in some cases, even today, earthquake locations remain poorly constrained (poor azimuthal distribution of stations, absence of stations close to the epicentre, simplified velocity model), and in most cases the focal depth is poorly determined. In these cases, without a surface break on a fault (e.g., the Teil earthquake of November 11, 2019 [Cornou et al., 2021]), accuracy of the instrumental location may be larger than 10 to 20 km. Sometimes, macroseismic data reveal major inconsistencies between the zones of highest intensity and the location of the instrumental epicentre that would otherwise have gone unnoticed. Going

back to the first half of the 20th century or even earlier, these data become essential, if not the only ones, for determining a “macroseismic epicentre” and the magnitude/depth of the earthquake in France [Cecić et al., 1996, Scotti et al., 2004, Musson and Cecić, 2012, Manchuel et al., 2018]. In the absence of a seismological station in the epicentral zone, the focal depth of small earthquakes can be apprehended by the pattern of macroseismic intensities around the epicentre [Traversa et al., 2018].

Many estimates of magnitude have solely been determined with the epicentral intensity parameter on epicentral intensity in the past. Indeed, the earthquake magnitude can be linearly related to the epicentral intensity because up to 1.25 Hz (corner frequency of the Wood Anderson seismograph with which the Richter magnitude has been originally defined) of the output signal is proportional to the ground acceleration [e.g. Aki and Richards, 1980]. Peak acceleration can thus be considered as proportional to intensity (see GMICE section below). However, the intensity at the epicentre, $I_0$ is often derived by interpolation from surrounding observations. It is also sensitive to site effects and the depth of the hypocentre. For this reason, $I_0$ is by far not the best parameter for assessing magnitude of historical or contemporary earthquake, but it is often the only one when there are few observations available. Other parameters, such as the radius of iso-intensity lines, are more robust when available [Frankel, 1994, Cara et al., 2008]. Depending on the available data, Traversa et al. [2018] selected different methods for estimating the moment magnitudes Mw of past earthquakes that were used for the seismicity catalogue FCAT-17 of metropolitan France [Manchuel et al., 2018].
## 4.2. Regional attenuation laws

Concerning attenuation properties, macroseismic data have made possible the identification of strong differences between regions of metropolitan France [Bakun and Scotti, 2006, Baumont et al., 2018] which were not clearly quantified in instrumental data because, until recently [Mayor et al., 2018], instruments were concentrated in border regions of the Alps, the Rhine graben and the Pyrenees. These results on various attenuation characteristics are, for example, confirmed by the macroseismic and instrumental observations of recent earthquakes of magnitude >4 located in western France [Sira et al., 2016a, Sira and Schaming, 2018, Sira et al., 2019].

In 2004, after the Saintes earthquake in Guadeloupe [Cara et al., 2005a—I<sub>max</sub> VIII in the commune of Terre-de-Haut], Beauducel et al. [2011] set up a simple attenuation model for French West Indies based on instrumental data with 13 accelerometric stations (magnitude, hypocentral distance, and peak ground acceleration (PGA)). On the basis of PGA-intensity relationships, they set up for the first time in France semi-automatic information specifying the probable intensities just after the occurrence of an earthquake.

## 4.3. Intensities versus instrumental ground motion parameters

For a wider use of the numerous macroseismic data, by coupling them with instrumental data, it is necessary to establish conversion laws between instrumental and macroseismic observations (GMICE). As early as 1904, Cancani indicates a factor of 2 in the PGA difference between two degrees of intensity. Many relationships published since then are the subject of numerous comparisons [Caprio et al., 2015]. The most frequently used conversions are with PGA, but Lesueur et al. [2013] show a better correlation between intensities and peak ground velocity (PGV). On the other hand, Atkinson and Sonley [2000] from California data and Souriau [2006] from French data identify a dependence with the epipentral distance for the PGA—Intensity relationship due to the modification of the frequency content, and thus a frequency dependence of the regional attenuation characteristics. The recent study of Mayor et al. [2018] shows that considering a realistic 2-D

distribution of absorption will improve the macroseismic intensity attenuation models.

## 4.4. Site effects

Site effects are included in macroseismic observations and the intensities determined according to modern macroseismic scales. Hence various attempts are made to identify them. They first need to identify the intensities not “at the rock” and those potentially affected by topographic site effects. This can be envisaged when there is precise geolocation of individual testimonies allowing cross-checking with large-scale (at least 1/50,000) local geological or topographical data. But this becomes a challenge with communal data, mostly located in both rocky and sedimentary areas, in varying proportions [Cara et al., 2007]. This is a clear limitation in site effects studies that cross-cut communal intensities, which are located at the official commune coordinate single point, with geological maps. The results from studies using small-scale geological data, as in Bossu et al. [2000] based on 1/1000,000 scale geological map, should be considered irrelevant. However, these local effects are sometimes visible during post-seismic macroseismic field studies (GIM) with variability between sediment and rock zones within the same commune. They are currently represented at BCSF-Rénass by double intensity levels for the same commune (e.g., V–VI or VI–VII). This double value can mean an uncertainty between two intensity values or for estimates from precise field observations, one or the other value is present in the municipality (this can indicate local site effects). Despite the EMS-98 rule to indicate the lower value, the BCSF has chosen to keep the indication of the double values to allow a better link with the estimates using past scales (MSK-64 in particular). While it is easy to convert half values to lower values, the reverse is not.

## 4.5. Seismic hazard investigations and seismic zonation

Seismic hazard investigations strongly rely on seismicity catalogues that must be as complete as possible and should cover as long time as possible. For metropolitan France, Rothé [1967] took up the macro- and microseismic data covering the period 1021–1960 in a first attempt to create a
seismotectonic map. The Perrey catalogues [e.g., Perrey, 1845] as well as 1650 documents of BCSF archives were incorporated in his study. For each earthquake, the maximum intensity is indicated and is associated with a known geological accident. The double chronological and geographical file issued from Rothé's work became the main source of information for the first French seismic code (rules PS-64). Today, probabilistic and deterministic seismic hazard studies still strongly rely on macroseismic intensities. The most recently published seismicity catalogue based on macroseismic and instrumental data is the FCAT-17 catalogue [Manchuel et al., 2018], and the comparison between the macroseismic intensities of metropolitan France with a European probabilistic seismic hazard model has been made by Rey et al. [2018]. The intensities are, for instance, used in the deterministic approach [Scotti et al., 2014] for nuclear facilities safety rules [ASN, 2001, RFS-2001-01] and for the hazard studies to produce the regulatory seismic zone map (last French decree in 2010).

## 4.6. Shakemaps based on macroseismic and instrumental data

The first rapid shakemap calculations were initiated by the TriNet project [Wald et al., 1997], thanks to the very rapid availability of instrumental data in California, mainly for crisis management purposes. The USGS quickly distributed a “ShakeMap” programme for operational computation [Wald et al., 2005] that is used worldwide. The macroseismic intensities derived from the “USGS-Did You Feel It” online form quickly appeared to be relevant [Atkinson and Wald, 2007] and led the USGS to develop version 3.5 of the ShakeMap programme. This version was implemented in France since 2012 [Masson et al., 2021]. Macroseismic intensities collected in France from Internet testimonials on www.franceseisme.fr are integrated and shared with the scientific community via an API from the first minutes after the event. They provide major spatial information, particularly in the first 50 km, with a ratio of up to a hundred between the number of communal intensities and instrumental measurements. As soon as earthquakes occur and for crisis management, the shakemaps deduced in particular from the preliminary intensities make it possible to rapidly model damage if one has knowledge of the vulnerability of buildings in the

affected zones [Guérin-Marthe et al., 2021]. Beyond crisis management, the final intensities derived from the communal questionnaires and the field mission can be used to produce a reference shakemap for the event.

## 4.7. Intensities and official recognition of natural disaster

In case of major damage, BCSF-Rénass is officially in charge of determining the communal macroseismic intensities in the area affected by damages within a short period of time and to transmit them to the Department of Civil Defence and Emergency Preparedness. This department is in charge of the natural disaster classification for insurance involvement in France. Through this procedure, BCSF-Rénass has been the reference player for 33 years. The work is mostly based on field investigations for the precise estimation of degree of damage to buildings by vulnerability classes EMS-98.

## 4.8. Seismic risk studies

Macroseismic intensities, linking building vulnerability and damage through a simplified three-level statistical approach [few, many, most Grünthal, 1998] are used to predict damage, notably via the Risk-EU conversion matrices [Milutinovic and Trendafiloski, 2003]. Thus, within the framework of crisis preparedness or seismic risk awareness, the impact of the intensities of some historical earthquakes in France can be used to simulate the level of damages and cost in the current urban areas by considering the evolution of vulnerabilities [Lambesc earthquake 1909, Riedel et al., 2014].

## 4.9. Media information, public awareness, and education

Macroseismic data have been available online for nearly 20 years, enabling effective participatory science to be engaged in a win-win relationship. Internet users inform the scientists who return to them, via the website or the media, the results of the analysed testimonies. Nearly 116,000 testimonies from citizens, including 15,000 from overseas departments, have been collected since 2000. Visits to the website www.franceseisme and the social networks
pages by the public show their interest for a better knowledge of telluric phenomena. Better understood, the seismic risk is thus better considered by the citizens and elected officials who are better able to measure the importance of respecting appropriate behaviours and seismic building regulations.

**5. Perspectives and evolutions**

Macroseismic studies experienced less and less scientific interest in the second half of the 20th century, when earthquake phenomenon became more and more understood, thanks to instrumental development, in particular with the accelerometric networks. However, since 1970, more quantitative information can be gathered from macroseismic data, first due to the improvement of intensity scales, with MSK-64 and then EMS-98, and second with the use of other indicators of the ground motion, such as “vibratory motion” felt by witnesses or “displacement and falling object”, which are clearly frequency-dependent sensors [Lesueur et al., 2013]. Although there is still room for improvement in the description of seismic effects according to intensity levels, in relation to the magnitude and distance from the epicentre, considerable progress has been made at BCSF since the time when a first seismicity map of France was presented by Jean-Pierre Rothé in 1937 (Figure 16). A comparison with the map of maximum intensities covering the period 1920–2020 in metropolitan France (Figure 17) illustrates the progresses made in both the number and quality of macroseismic data.

Given new methods of information collection (individual and communal internet questionnaires, social networks, field expertise) and analysis (data mining algorithms on testimonies or press articles), the amount of accessible information becomes an important resource for updating intensity scales and for supplementing the necessarily scattered information from the accelerometric networks.

Information collection can be improved and several challenges remain to be addressed. A balance needs to be found between the classical questionnaires (individual or communal) that are very informative but time-consuming to fill in, and simplified questionnaires less reliable and informative, that can cover the affected area with more numerous data points but reduce the reliability of the response and

the accuracy of observation. Complete and accurate information remains essential for the studies of indicators properties and the improvement of macroseismic scale and other tools. Concerning individual testimonies, a strategy that should be explored is also to rely on a panel of subscribed witnesses who can be called upon for each event, sufficiently representative at the municipal level. This would allow us to avoid working only with spontaneous reports, mainly positive and too often in small numbers in case of weak tremors.

Data analysis can also benefit from significant improvements through the implementation of automatic response processing using expert systems [Musson, 2006]. This can save time and increase the reliability and homogeneity of estimates, for rapid shakemap, for example. However, the subjectivity of the analysis will always be present, implicitly integrated in the programming of the response processing algorithm.

The drawing of the isoseists remains another important issue to be better addressed in the future. Even if the use of digital interpolation programmes has made it possible to considerably reduce human subjectivity in plotting, the various parameters included in the interpolation must be made accessible in the metadata of this procedure, in order to better take into account the possible biases of these calculations: geographical distribution of the data used, interpolation methods and parameters used, discretization thresholds, variogramme, etc. Thus enlightened, the plot of isoseists, more or less generalized or simplified, can be selected according to the uses sought [Bormann, 2012]. These “biases” could be positively used as uncertainties on the results by multiplying the computation with all possible parameters.

Given the often cross-border nature of seismic effects in France, it remains also important to pursue the efforts undertaken when the European EMS-98 was set up. Overcoming administrative borders by facilitating the exchange of macroseismic data in a standardized format remains an essential task for the scientific community. Cross-border collaboration through the establishment of macroseismic expert groups (GIM-PYR project, pocrisc.eu, ESC working group, www.escmacroswg.rm.ingv.it/) and the use of similar survey methods is another challenge to improve cross-border macroseismic estimation.
<figure><img src="image_26.png" /><figcaption>**Figure 16.** Map of the distribution and extension of earthquakes in France. The different colours do not have any special meanings and are intended to make it possible to distinguish the areas of the extensions of the main earthquakes for the years 1925–1936. [Rothé, 1937] (with gracious authorization of Hatier edition).</figcaption></figure>

An effort must be made in the future to better characterize the macroseismic data with metadata specifying the version of the survey questionnaire, the number of data used, the type of source (questionnaires, press article, spontaneous letter...),

the type of information on vulnerability used for the damage analysis, the upper and lower bounds of possible intensities with the preferential value, etc. These are all key points necessary and requested by users for a better use of macroseismic databases.
Maximum communal intensities from 1920 to 2020.
BCSF-RENASS database (Dec. 2020 version)

<figure><img src="image_27.png" /><figcaption>**Figure 17.** Maximum communal intensities from 1920 to 2020 (BCSF-Rénass database-December 2020).</figcaption></figure>

Exploration of BCSF archives since 1921 shows that some of our data are not yet fully exploited. This is the case of unpublished maps, photos of some building damages, or some personal archives (Jean Vogt for BRGM and Pierre Stahl for the Pyrenean earthquakes). The ongoing digitization of BCSF archives complementing digitizations performed in various organizations (national, university, notary, or press archives...), will help facilitate further studies. New methods of documentary research, such as research in press archives, character recognition and keyword searches, will also make it possible to identify felt earthquakes that have not yet been catalogued.

All the work currently being carried out by the BCSF-Rénass to improve the methods for collecting macroseismic data, analysis, and dissemination of information is discussed within the Research Infrastructure Resif-Epos in the Transverse Seismicity Action [Masson et al., 2021].
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