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1 Lehr- und Forschungsgebiet Neotektonik und Georisiken, Geowissenschaften, RWTH Aachen, Lochnerstr. 4-20, D-52064 Aachen, Germany
2 Dipartimento di Scienze Chimiche e Ambientali, Università del
Insubria, Via Valleggio 11, 22100 Como, Italy
3 Departamento de Geología, Universidad de Salamanca, Escuela Politécnica Superior de Ávila, Avda. Hornos Caleros, 50. 05003-Ávila, Spain
* Corresponding author (e-mail: k.reicherter{at}nug.rwth-aachen.de)
This volume grew particularly out of two meetings held in 2006 (European Geosciences Union General Assembly 2006, Session TS4.4, ‘3000 years of earthquake ground effects in Europe: geological analysis of active faults and benefits for hazard assessment’, Vienna, Austria, April 2006; and the ICTP/IAEA workshop on ‘The conduct of seismic hazard analyses for critical facilities’, Trieste, Italy, May 2006) that brought together geoscientists who have explored and studied palaeoseismicity and its environmental effects in several parts of the world. This publication contains 18 papers based on a selection of presentations, and addresses a wide range of topics related to both a) palaeoseismological studies, and b) the assessment of a new macroseismic intensity scale based only on the natural phenomena associated with an earthquake, that is the ESI 2007 scale.
In 1999, during the 15th INQUA (International Union for Quaternary Research) Congress in Durban, the Subcommission on Palaeoseismicity promoted the compilation of a new scale of macroseismic intensity based only on environmental effects. A working group including geologists, seismologists and engineers compiled a first version of the scale that was presented at the 16th INQUA Congress in Reno in 2003, and updated one year later at the 32nd International Geological Congress in Florence (Michetti et al. 2004). To this end, the INQUA TERPRO (Commission on Terrestrial Processes) approved a specific project (INQUA Scale Project 2007). The revised version was ratified during the 17th INQUA Congress in Cairns in 2007. This revised version of the scale, which is formally named the Environmental Seismic Intensity scale–ESI 2007, is composed of two parts.
The main advantage of the ESI 2007 scale is the classification, quantification and measurement of several known geological, hydrological, botanical and geomorphic features for different intensity degrees, differentiating two main categories of earthquake effects on the environment: (a) primary (fault surface ruptures and tectonic uplift/subsidence); and (b) secondary (including ground cracks, slope movements, liquefaction processes, anomalous waves and tsunamis, hydrogeological anomalies, and tree shaking). Primary effects triggered by surface faulting are almost absent for intensity degrees below VIII, are characteristic, but moderate for intensities between VIII and X, and diagnostic for the stronger top intensities of XI and XII (Fig. 1). This differentiation subdivides the earthquakes into three main categories (A, B, C), in which the absence (A), occurrence (B) and dimensions (B, C) of fault surface offsets allow the assignment of intensity to present and past seismic events. Complementarily, the dimension (width, length, volume of mobilized material) of secondary effects allows intensities to be constrained for type A and B earthquakes; while the extension of the area affected by secondary effects allows assessment of the epicentral intensity for type A, B and C earthquakes. Secondary effects are typically diagnostic for type B earthquakes, but frequently saturate for type C. In the same way primary effects are diagnostic for type C earthquakes, when structural damage to human constructions and engineering facilities saturate. In principle, both the total area affected by secondary effects and the dimensions (surface rupture length, displacement, amount of coseismic uplift or subsidence) of primary effects do not saturate for the large earthquakes. The combination of the ESI 2007 scale with other classic intensity scales (MSK, EMS, MM, MCS) helps to compare recorded structural damage with the dimension of observed or reported (past earthquakes) environmental effects, and consequently exports the obtained seismic records to past prehistoric events. Figure 1 summarizes the ESI 2007 chart (Silva et al. 2008), which illustrates the different categories of earthquakes as well as the main characteristic features for the different types of effects. Also, this chart gives a qualitative approach for the affected areas, type of geological and geomorphologic record, and their respective degree of preservation through time.
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The authors of this introduction do not ignore, however, that the use of macroseismic effects on natural surroundings is controversial. Over the past 40 years at least, proper attention has not been paid to these effects in estimating intensity, because they were reputed to be too variable, and likewise because they were not properly weighted in the scales. For example, recent data indicate that some phenomena occur, or start to occur, at degrees other than the ones they are assigned to in the scales: liquefaction, for instance, starts at lower intensities (VI–VII, or even V; e.g. Keefer 1984; Galli 2000; Porfido et al. 2002; Rodriguez et al. 2002) and not at VII or IX as indicated in most scales. We argue that the existence of similar inconsistencies in the available macroseismic scales should not lead to the conclusion that ground effects are useless for assessing earthquake intensity.
These uncertainties lead to an increasing lack of confidence in using ground effects as diagnostics, and progressively the effects on human perception and the anthropic environment (mainly buildings) became the only sensors analysed for intensity assessment. Exemplifying this logic, in the latest proposal by the European Seismological Commission to revise the MSK scale (Grünthal 1998), these effects are not reported in the scale per se, only in a brief appendix. We believe, however, that if this orientation is pursued, intensity will come to reflect mainly the economic development of the area that experienced the earthquake instead of its ‘strength’ (Serva 1994). It is also our belief that by ignoring ground effects, it will not be possible to assess intensity accurately in sparsely populated areas and/or areas inhabited by people with different modes of existence, such as nomads. This point has been very clearly made by Dengler & McPherson (1993). The ESI scale is the logical extension of their approach. Furthermore the main problems arise for the highest degrees, XI and XII, where ground effects are the only ones that permit a reliable measurement of the severity of earthquake. All the scales, in fact, show that in this range of intensity ground effects predominate.
We believe the new ESI 2007 scale needs wider dissemination to allow a full scientific debate about its application to take place. One of the purposes of this Special Publication is thus to open the debate on a ‘ground effects’ scale for seismic hazard assessment.
It should be noted that the motivation for a new intensity scale based only on one class of macroseismic information, the effects on nature, rests exactly on the dramatic progress of our knowledge about the coseismic ground effects, and notably about surface faulting, gained in the last 30 years thanks to the growth of palaeoseismological studies. In the monograph Active Tectonics: Impacts on Society (Wallace 1986), the first book that can be regarded as an overview of palaeoseismology, several papers made absolutely clear the quantitative relations that link the physical phenomena induced by earthquakes in the natural environment and the earthquake size. It has become a global, standard practice for palaeoseismologists since the late 1970s to survey in the field immediately after an earthquake the distribution of landslides, liquefactions, hydrological changes, coastal uplift and subsidence, and especially the characters and dimensions of tectonic ground ruptures. This is particularly true for the environmental effects generated by large earthquakes that break the ground surface (e.g. Allen 1986). Today, for instance, we have about 40 large earthquakes for which the geometry of surface faulting and the slip distribution along the fault strike have been mapped in detail (Wesnousky 2008). In this way, ground effects can be estimated from observations and regression analyses of historical earthquakes and a) fault displacement (Slemmons & dePolo 1986), b) liquefaction (Galli 2000), c) landslides (Keefer 1984), and several other features. This knowledge was not available at the time of early macroseismic scales, which very wisely included environmental effects in the different intensity degrees, but obviously without a detailed quantitative description due to the poor available dataset. There now exists an entirely new catalogue of information that allows us to update the macroseismic intensity observations by incorporating a wealth of palaeoseismological data. Vice-versa, the new macroseismic intensity scale based on environmental effects becomes a valuable tool and a guide for the palaeoseismologist. The lessons learned from intensity observations are educational for palaeoseismic analyses and interpretations, because they encourage the specialist to cross-check the results obtained using one particular evidence of palaeoseismicity. Once an ESI 2007 intensity degree has been assessed from a particular palaeoseismic feature, consistency with the whole spectrum of ground effects included in the same intensity degree should be ensured.
In our opinion, this illustrates quite well the scope of the present Special Publication and the basic idea behind all the presented contributions. The volume is divided into two sections. The first section focuses on the analysis of the coseismic ground effects from contemporary and historical earthquakes, and the implementation and refinement of the ESI 2007 scale. The second section is devoted to the analysis of individual case histories illustrating the different geological, geomorphological, geophysical techniques and field-survey methods used to identify causative and capable faults, and seismic hazard, from seismological and palaeoseismological approaches.
Papanikolaou et al. revise the macroseismic information for several earthquakes in Greece in order to calibrate the ESI 2007 scale against the traditional, damage-based scales. Their results show how the ESI 2007 scale, following the same criteria for all earthquakes, can compare not only events from different settings, but also contemporary and future earthquakes with historical events. This is of particular value for seismic hazard assessment in countries with a long record of seismicity such as Greece.
Two papers take advantage of a very large number of fault trench exposures to draw inference on earthquake hazard and fault behaviour along major strike-slip structures. Rockwell et al. illustrate extensive fault trenching across the trace of the coseismic ground ruptures associated with the large earthquakes of 9 August 1912 and 17 August 1999 along the North Anatolian Fault, west and east of the Marmara Sea, respectively. This allows better resolution of the history of surface ruptures for the past 400 years around Istanbul. A better quantitative assessment of coseismic environmental effects such as fault displacement is critical for the mitigation of earthquake risk in one of the largest metropolitan areas of the Earth.
Mouslopoulou et al. use fault data from 20 trenches to explore whether changes in late Quaternary fault kinematics principally arise due to earthquake rupture arrest and/or variations in slip vector pitch during individual earthquakes that span the kinematic transition zone occurring along the North Island Fault System, New Zealand, near the intersection with the active Taupo Rift.
Ground effects from four large earthquakes in Japan and Taiwan have been compiled by Ota et al. in order to assess the ESI 2007 scale. The new resulting maps show more detailed intensity patterns than those previously available for the four areas. Calibration exercise also reveals, however, that the ESI 2007 intensity scale needs some methodological improvement. This is somewhat expected and is needed for the better implementation of this new intensity scale in the future.
A similar exercise is proposed by Tatevossian et al., who used examples from the Altai (27 September 2003) and the Neftegorsk (27 May 1995) earthquakes. One of the main points made by these authors is the relevance of the environmental effects for intensity assessment in the near field of strong earthquakes. We argue that this is the very fundamental concept which provides reliable relations between palaeoseismology, macroseismic intensity and seismic hazard assessment. The results of Tatevossian et al. should be compared with those presented by Ota et al., Mosquera-Machado et al. and Zahid et al. The epicentral intensity (I0) based on the ESI 2007 scale can be two to four times higher than I0 assessed without taking into account the ground effects. This indicates that by excluding the environmental effects, especially primary effects, we not only miss a valuable piece of information, sometimes the only one available in sparsely populated areas, but we are also missing the low frequency (static) part of an earthquake impact. In the epicentral area of strong seismic events, where the static offset reaches the order of several metres, intensity assessments ignoring this component are useless.
The integrated identification and analysis of archeoseismic and palaeoseismic evidence at the Roman site of Baelo Claudia, Gibraltar Strait (south Spain), is the purpose of the work by Silva et al. These authors combine observations on damage and secondary environmental effects in order to assess the local seismic hazard in terms of expected recurrence of intensity values within a specific time window.
A similar potential archeoseismic case history in a region with moderate seismicity is presented by Hinzen & Weiner, who apply geotechnical modelling to test the coseismic hypthesis for the damage to a Neolithic wooden well recently excavated near Erkelenz, in the Lower Rhine Embayment (NW Germany).
Two papers revise earthquake ground effects and active faulting in sparsely populated regions. Mosquera-Machado et al. studied the Mw 7.3 Murindo earthquake (18 October 1992) in NW Colombia, which provides relevant data for the application of the ESI 2007 scale. The resulting new isoseismal map is relevant for the assessment of future seismic risk in this part of Colombia where intensity assessment based on traditional damage-based scales cannot give a detailed picture of the earthquake severity. The Mw 7.8 Kunlun earthquake (14 November 2001) occurred in northern Tibet, in a remote, high-mountain region. Lin & Guo documented for the first time the palaeoseismic history of this region based on evidence of liquefaction within the trace of the 450-km-long surface rupture zone generated by this large event.
The analysis of the coseismic effects on the natural environment along the 110-km-long zone of surface thrust faulting associated with the M 7.6 Muzaffarabad, Pakistan, earthquake of 8 October 2005, is the topic covered by Ali et al., also discussed from the seismotectonic point of view by MonaLisa. The macroseismic intensity distribution for this event shows a remarkable correlation with the trace of the surface rupture. Near Muzaffarabad, intensity XI in the MM, EMS-98 and ESI 2007 scales has been consistently assessed at sites where maximum values of fault displacement (in the order of 4 m) were observed.
Both Gregersen & Voss and Mörner provide a comprehensive seismological and palaeoseismological framework for the understanding and interpretation, in terms of seismic hazard, of the remarkable evidence of post-glacial palaeoseismicity available in Scandinavia.
A particular category of ground effects, that is found in the endokarstic terrains, is explored by Pérez-López et al., starting from the observation of the collapse that occurred within the Benis Cave (–213 m; Murcia, SE Spain), during the Mula earthquake (mb=4.8, MSK VII, 2 February 1999).
Also in SE Spain (Almería Region), the stratigraphic and sedimentological evidence of past tsunamis in the western Mediterranean is discussed by Reicherter & Becker-Heidmann. The authors used shallow drilling in the lagoon of Cabo de Gata for identifying possible tsunamites associated with the 1522 Almería earthquake.
Trenching along the Vilariça segment of the Manteigas-Bragança Fault in NE Portugal, allows Rockwell et al. to identify evidence of a cluster of surface faulting earthquakes in the latest Pleistocene to early Holocene. This holds relevant implications for the seismic hazard of this region, characterized by moderate historical seismicity. Likewise, White et al. discuss the evidence for recent activity and related seismic hazard along the Hebron Fault in SW Namibia, within a stable continental area.
In summary, the set of papers included in this volume is basically devoted to the analysis of environmental earthquake effects linked to recent, past and prehistoric strong seismic events. The understanding of the type and dimensions of earthquake ground effects linked to different levels of seismic shaking and earthquake magnitude is the only prudent and consistent way to incorporate past strong events, only witnessed in the geological and geomorphological record, into the classic seismic catalogues, which are the basis of most of the seismic hazard studies and assessments. The efforts of the palaeoseismological community are directed to expanding back in time, and refining in terms of completeness, the seismic history of individual faults and/or seismic regions, in order to achieve a better understanding of the pulse (regularity and/or clustering) of seismic cycles in different tectonic settings, and its further implementation in hazard studies. Although the ESI 2007 scale is properly devoted to its application to past earthquakes, its application to recent events is critical, since it will allow refining the scale, and therefore improving maximum intensities recorded during past events. This volume offers to the scientific community a new tool to assign intensities, and a wide variety of geological methods to identify and measure earthquake environmental effects.
Appendix: ESI 2007 scale definition of intensity degrees
Text in italic indicates effects that can be used directly to define an intensity degree.
From I to III.
There are no environmental effects that can be used as diagnostic.
IV Largely observed/First unequivocal effects in the environment.
Primary effects are absent.
Secondary effects
V Strong/Marginal effects in the environment.
Primary effects are absent.
Secondary effects
VI Slightly damaging/Modest effects in the environment.
Primary effects are absent.
Secondary effects
VII Damaging/Appreciable effects in the environment.
Primary effects observed very rarely, and almost exclusively in volcanic areas. Limited surface fault ruptures, tens to hundreds of metres long and with centimetric offset, may occur, essentially associated with very shallow earthquakes.
Secondary effects. The total affected area is in the order of 10 km2.
VIII Heavily damaging/Extensive effects in the environment.
Primary effects are observed rarely.
Ground ruptures (surface faulting) may develop, up to several hundred metres long, with offsets not exceeding a few centimetres, particularly for very shallow focus earthquakes such as those common in volcanic areas. Tectonic subsidence or uplift of the ground surface with maximum values on the order of a few centimetres may occur.
Secondary effects. The total affected area is in the order of 100 km2.
IX Destructive/Effects in the environment are a widespread source of considerable hazard and become important for intensity assessment.
Primary effects are observed commonly.
Ground ruptures (surface faulting) develop, up to a few kilometres long, with offsets generally in the order of several centimetres. Tectonic subsidence or uplift of the ground surface with maximum values in the order of a few decimetres may occur.
Secondary effects. The total affected area is in the order of 1000 km2.
X Very destructive/Effects on the environment become a leading source of hazard and are critical for intensity assessment.
Primary effects become leading.
Surface faulting can extend for a few tens of kilometres, with offsets from tens of centimetres up to a few metres. Gravity grabens and elongated depressions develop; for very shallow focus earthquakes in volcanic areas rupture lengths might be much lower. Tectonic subsidence or uplift of the ground surface with maximum values in the order of a few metres may occur.
Secondary effects. The total affected area is in the order of 5000 km2.
XI Devastating/Effects on the environment become decisive for intensity assessment, due to saturation of structural damage.
Primary effects are dominant.
Surface faulting extends from several tens of kilometres up to more than one hundred kilometres, accompanied by offsets reaching several metres. Gravity graben, elongated depressions and pressure ridges develop. Drainage lines can be seriously offset. Tectonic subsidence or uplift of the ground surface with maximum values in the order of numerous metres may occur.
Secondary effects. The total affected area is in the order of 10 000 km2.
XII Completely devastating/Effects in the environment are the only tool for intensity assessment.
Primary effects are dominant.
Surface faulting is at least a few hundreds of kilometres long, accompanied by offsets reaching several tens of metres. Gravity graben, elongated depressions and pressure ridges develop. Drainage lines can be seriously offset. Landscape and geomorphological changes induced by primary effects can attain extraordinary extent and size (typical examples are the uplift or subsidence of coastlines by several metres, appearance or disappearance from sight of significant landscape elements, rivers changing course, origination of waterfalls, formation or disappearance of lakes).
Secondary effects. The total affected area is in the order of 50 000 km2 and more.
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