The Database of Coseismic Environmental Effects as a Tool for Earthquake Intensity Assessment within the INQUA EEE Scale Project
by
Luca Guerrieri
APAT (Italian Agency for Environment Protection and Technical Services), via Vitaliano Brancati 48, 00144 Roma
Coauthors: Ruben Tatevossian, Eutizio Vittori, Valerio Comerci, Eliana Esposito, Alessandro M. Michetti, Sabina Porfido, Leonello Serva

Refining the record of relevant Holocene natural events, and therefore of past seismicity, is one of the goal of the Dark Nature Project. Hazard forecast and risk mitigation must be based on high-resolution paleo-records. In this paper, we discuss new methodological approaches for the study of earthquake ground effects, allowing a better comparison between seismological and paleoseismological evidence.

In the last years, scientists dealing with seismic hazard assessment have started to acknowledge the potential substantial role of earthquake environmental effects (EEE) for earthquake intensity assessment. In fact it has become evident that EEEs should be taken into account for the following reasons:

i) compared to traditional macroseismic scales, they ensure a higher comparability at the global scale, as EEEs are free from the influence of cultural and technological aspects;

ii) all the effects on humans commonly used to calibrate intensity of shaking, suffer from saturation beyond intensity IX-X of the modern 12-degrees macroseismic scales;

iii) they allow to extend the time span of earthquake catalogues to prehistoric times. In fact, surface faulting and other secondary effects (principally liquefaction) related to prehistoric events can be in some cases dated and sized through detailed paleoseismological investigations.

In 1999, based on these general statements, an international group of geologists, seismologists and engineers promoted the compilation of a new scale of intensities based only on environmental effects (EEE Scale). A draft version of this scale was presented at the 14th INQUA Congress in Reno (2003), after an appraisal of the environmental effects induced by about 150 earthquakes distributed worldwide. A first update came one year later (Michetti et al., 2004) at the 32nd IGC in Florence.

A 4-years long international project (2003-2007) approved by INQUA and carried out by the INQUA TERPRO SubCommission on Paleoseismicity, http://www.apat.gov.it/site/en-GB/Projects/INQUA_Scale/default.html) is revising the present version of the scale, by analyzing the EEEs triggered by recent and historical earthquakes. In particular, several Regional Working Groups are testing the scale with well-documented seismic events occurred in their country. The ultimate goal of the project is to present the final version of the scale at the 15th INQUA Congress (in Cairns in 2007).

Either coseismic environmental effects and man-made structures are strongly influenced by the site stratigraphy and morphology. In general, as commonly occurred for the conventional macroseismic scales applied to historical events (MM, MCS and partly MSK), the local EEE intensity value is attributed through an "expert" evaluation based on the description reported in the scale for that specific effect, i.e., without the statistical approach followed by the most recent conventional scale (EMS).

Wherever possible, the local EEE intensity should be evaluated taking into account not the single effect, which typically occurs at a site, but all the effects observed within a limited area of "uniform" geology (locality), for example a river valley, mountain slope, large hill, a village or part of it, etc.. Therefore, the archiving process should be done at two levels of progressive detail (locality level and site level). In traditional macroseismic studies, the scale of locality level is typically a village, while a single macroseismic object (i.e. a single building), where damage degree can be defined but not intensity, is an analogue of site.

In order to ensure the objectivity of the testing procedure, participants to the project have agreed on the need to store information regarding EEEs into a database precisely defined in its structure and format, which follows the draft form initially adopted for the field survey. Actually, only a rigorous approach ensures the comparability of environmental effects triggered by earthquakes occurred in geologically and tectonically very different settings. This database, conceived as the tool to effectively store and retrieve information regarding past and new earthquakes by the participants to the project, is already accessible in the web page of the project and will be periodically updated with the contributes from the regional WGs.

The EEE database has a relational structure kept as simple as possible. Several masks facilitate the input of data, from the most general to the most detailed ones. There are four main tables in agreement with the logical approach of the EEE Scale. So, each record in the table "Earthquake" is associated with one-to-many records in the "Locality" sub-table and each record in "Locality" is associated to one-to-many records in its EEE Sites sub-table.

As the main table "Earthquake" presents general information on the seismic event, including surface faulting parameters, the table "Locality" reports all the information about the locality where one or more coseismic effects have occurred, i.e. location (coordinates, altitude) and local expression of the earthquake (e.g., local macroseismic intensity, site PGA).

The table "Site" summaries the characteristics of the site (location, geomorphological environment, etc.) and the type of effect (surface faulting, slope movements, ground cracks, ground settlements, hydrological anomalies, tsunami, not geological effects). Information about the effect size, as requested in the EEE scale, can be archived in detail according to the type of effect. Information about damages on man-made structures (buildings, bridges, roads, etc.) in the same site, can be archived in a proper table "Effects on man-made structures". In order to standardize the descriptions of the effect and the site, data input is helped through the selection of attributes from a predefined menu.

Finally, it is possible to assess the range of EEE intensities (minimum and maximum values) compatible with the size of the effect and its features. As the data input for a locality has been completed, it is possible to assess the EEE intensity for that locality on the basis of all EEE effects occurred within that locality.

Moreover, in order to map the field of EEE local intensities, the EEE database allows to generate a table of localities with coordinates and EEE local intensities, that can be exported and loaded on a GIS project.

In addition, a proper "EEE form" devoted to field annotations immediately after a seismic event has been prepared, due to the common difficulty to work directly with a database directly in the field during an emergency. This form contains the same fields and structure of the EEE database.

Reference

A.M. Michetti, E. Esposito, A.Gurpinar, B. Mohammadioun, J.Mohammadioun, S. Porfido, E. Roghozin, L. Serva, R. Tatevossian, E.Vittori, F. Audemard, V. Comerci, S. Marco, J. McCalpin, N.A. Morner (2004). The INQUA Scale. An innovative approach for assessing earthquake intensities based on seismically induced ground effects in natural environment. Memorie Descrittive della Carta Geologica d'Italia, Special Volume LXVII, E. Vittori and V. Comerci eds.. APAT-Dip. Difesa del Suolo/ Servizio Geologico d'Italia. Roma.

Date received: July 13, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-28.