Luca Guerrieri

Pattern and Rates of Faulting in the Central Nevada Seismic Belt, and Paleoseismic Evidence for Prior Beltlike Behavior

The central Nevada seismic belt (CNSB) is a concentration of historical (1915-1932-1954) surface faulting in the western Basin and Range province, forming a linear, nearly continuous 300-km-long rupture zone. Previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older, similar beltlike patterns or elevated slip rates that could indicate whether the CNSB is a zone of focused, long-term crustal strain. The data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record. At the 1954 Fairview Peak fault, the lack of prehistorical faulting in deposits containing the Wilson Creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35.4 ka. Our studies also show that the faults have net slip rates ranging from a low of 0.09 mm/yr on the Fairview Peak fault to a high of 0.7 mm/yr on the 1932 Cedar Mountain fault. These are considered moderate to low rates that are similar to most late Quaternary faults in the western Basin and Range province. A space-time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse, and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults. Based on these results we reach several conclusions regarding the longer term (≈Holocene) behavior of the CNSB. Although paleoseismic data preclude an older identical rupture belt among the historical zones, consideration of associated Holocene faults within the greater CNSB region indicates that several similar, but not identical, beltlike rupture patterns are plausible during the past 13 ka, although each requires seismic gaps in the along-strike pattern. Although long-term strain (represented by density of young faults) does appear to increase from east to west into the CNSB, the slip-rate data demonstrate that the CNSB is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the Sierra Nevada. The increase in the distribution of Holocene fault activity from east to west into the CNSB is consistent with a marked increase in the 1992-2002 GPS velocity field at the latitude of the 1954 rupture sequence. However, a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates (0.59-1.37 mm/yr) are systematically lower than both the campaign and continuous GPS rates (2.20-3.13 mm/yr) by factors of 2-5. These discrepancies may be due to postseismic strain, or to some form of off-fault deformation. We conclude that the results of our study of fault behavior in the CNSB best support the belt migration model proposed by Wallace (1987) for the western Basin and Range province in which temporal tectonic pulses are believed to migrate regionally, activating different beltlike combinations of late Quaternary faults in an as yet unknown pattern of migration.

Surface Faulting of the 6 April 2009 Mw 6.3 L’Aquila Earthquake in Central Italy

This paper documents evidence of surface faulting associated with the 6 April 2009 moderate-sized earthquake (ML 5.8, Mw 6.3) in the central Apennines of Italy, which caused major damage to the town of L’Aquila and its surroundings. Coseismic surface ruptures were mapped for a minimum distance of 2.6 km along the Paganica fault, a fault still poorly investigated relative to the other active faults nearby, which bound much wider range fronts. Surface rupture length (SRL) and maximum displacement parameters (2.6 km minimum and 10–15 cm, respectively) are in agreement with what is expected for an Mw 6.3 event in the Italian Apennines tectonic environment. Different viewpoints exist on the amount of SRL and the number of activated faults. We propose a pattern of sympathetic and secondary slip on an array of faults around the master seismogenic structure. Past seismicity and evidence for larger Holocene offsets on this and other capable faults nearby prove that the 2009 event is not a good reference event for assessing the seismic hazard of the region. Nevertheless, the 2009 L’Aquila earthquake once more confirmed the importance of detailed geological studies for a proper seismic hazard assessment, and it clearly illustrates the need to pay attention to moderate events and supposedly minor active faults. Indeed, this type of earthquake is rather frequent in the whole Mediterranean region and is potentially much more destructive than in the past, due to the expanding urban centers and infrastructures inside their epicentral regions and even right above the traces of capable faults.

AREAL DISTRIBUTION OF GROUND EFFECTS INDUCED BY STRONG EARTHQUAKES IN THE SOUTHERN APENNINES (ITALY)

Moderate to strong crustal earthquakes are generally accompanied by a distinctivepattern of coseismic geological phenomena, ranging from surface faulting to groundcracks, landslides, liquefaction/compaction, which leave a permanent mark in thelandscape. Therefore, the repetition of surface faulting earthquakes over a geologictime interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I = X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I = X MSK, Ms = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilinear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrologicalanomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes.

Possible evidence of paleomarsquakes from fallen boulder populations, Cerberus Fossae, Mars

In order to differentiate between boulder avalanche deposits triggered by temperature/climate controlled melting of ice or triggered by ground shaking produced by paleomarsquakes, spatial variation in boulder size populations has been measured from High Resolution Imaging Science Experiment (HiRISE) images along Cerberus Fossae, one of the youngest fracture/graben systems on the Martian surface. The boulders have fallen from less than ∼500 m high fault-controlled cliffs and rolled and bounced across relatively coarse-grained sediment, forming colluvial fans. The boulders have left trails in the dust in some cases, coming to rest on relatively fine-grained Aeolian sediment. The boulder size distribution varies along the graben contrary to what would be expected if boulder falls had been liberated by temperature/climate controlled melting of ice. Boulder size and boulder trail data peak close to the center of the fault system, decreasing along strike. Furthermore, evidence for relatively recent surface faulting of colluvial slopes along the fault-controlled cliffs is confined to the area with anomalously large boulder/trail size data. We interpret the above as consistent with observations of terrestrial earthquake-triggered boulder avalanches where boulder sizes decrease away from the epicenter and surface faulting. We discuss the implications of possible marsquakes along Cerberus Fossae in terms of active faulting associated with dike emplacement that is subradial to the Elysium Mons volcano.

Earthquake Hazard and the Environmental Seismic Intensity (ESI) Scale

The main objective of this paper was to introduce the Environmental Seismic Intensity scale (ESI), a new scale developed and tested by an interdisciplinary group of scientists (geologists, geophysicists and seismologists) in the frame of the International Union for Quaternary Research (INQUA) activities, to the widest community of earth scientists and engineers dealing with seismic hazard assessment. This scale defines earthquake intensity by taking into consideration the occurrence, size and areal distribution of earthquake environmental effects (EEE), including surface faulting, tectonic uplift and subsidence, landslides, rock falls, liquefaction, ground collapse and tsunami waves. Indeed, EEEs can significantly improve the evaluation of seismic intensity, which still remains a critical parameter for a realistic seismic hazard assessment, allowing to compare historical and modern earthquakes. Moreover, as shown by recent moderate to large earthquakes, geological effects often cause severe damage”; therefore, their consideration in the earthquake risk scenario is crucial for all stakeholders, especially urban planners, geotechnical and structural engineers, hazard analysts, civil protection agencies and insurance companies. The paper describes background and construction principles of the scale and presents some case studies in different continents and tectonic settings to illustrate its relevant benefits. ESI is normally used together with traditional intensity scales, which, unfortunately, tend to saturate in the highest degrees. In this case and in unpopulated areas, ESI offers a unique way for assessing a reliable earthquake intensity. Finally, yet importantly, the ESI scale also provides a very convenient guideline for the survey of EEEs in earthquake-stricken areas, ensuring they are catalogued in a complete and homogeneous manner.

Landslides Induced by Historical and Recent Earthquakes in Central-Southern Apennines (Italy): A Tool for Intensity Assessment and Seismic Hazard

Analysis of distribution of landslides (rock falls and coherent slides), induced by 12 moderate to strong earthquakes occurred in the last three centuries in Central–Southern Apennines, has permitted to investigate the relationship of their maximum distance versus magnitude and ESI epicentral intensity.

Quaternary geology and paleoseismology in the Fucino and L’Aquila basins

This 2 days-long field trip aims at exploring field evidence of active tectonics, paleoseismology and Quaternary geology in the Fucino and L’Aquila intermountain basins and adjacent areas, within the inner sector of Central Apennines, characterized by extensional tectonics since at least 3 Ma. Each basin is the result of repeated strong earthquakes over a geological time interval, where the 1915 and 2009 earthquakes are only the latest seismic events recorded respectively in the Fucino and L’Aquila areas. Paleoseismic investigations have found clear evidence of several past earthquakes in the Late Quaternary to Holocene period. Active tectonics has strongly imprinted also the long-term landscape evolution, as clearly shown by numerous geomorphic and stratigraphic features. Due to the very rich local historical and seismological database, and to the extensive Quaternary tectonics and earthquake geology research conducted in the last decades by several Italian and international teams, the area visited by this field trip is today one of the best studied paleoseismological field laboratories in the world. The Fucino and L’Aquila basins preserve excellent exposures of earthquake environmental effects (mainly surface faulting), their cumulative effect on the landscape, and their interaction with the urban history and environment. This is therefore a key region for understanding the role played by earthquake environmental effects in the Quaternary evolution of actively deforming regions, also as a major contribution to seismic risk mitigation strategies.

Surface Faulting Hazard in Italy: Towards a First Assessment Based on the ITHACA Database

The Italian territory is characterized by a great number of capable faults (i.e., faults able to produce significant ruptures/deformations at or near the surface). However, the potential of tectonic surface rupture/deformation (Surface Faulting Hazard, SFH) is not properly considered in national seismic hazard maps and legislation. In this paper it is proposed an assessment of SFH in Italy based on the ITHACA database, where the shape and width along capable faults as well as maximum expected surface displacements are defined in function of the seismotectonic behaviour and the severity of maximum expected earthquake. The proposed assessment indicates where SFH is expected to be relevant. In this sense, it is an helpful tool for site selection of critical facilities but also for ordinary land planning. Of course, the evaluation of SFH at local scale in the setback areas requires a more detailed characterization through ad hoc seismotectonic and paleoseismic investigations.

Landslides Induced by the 1908 Southern Calabria: Messina Earthquake (Southern Italy)

Five hundred and two different testimonies of coseismic environmental effects of the 1908 Southern Calabria-Messina earthquake have been identified and catalogued, based on a careful screening of contemporary documents, i.e. technical and photographic reports, newspapers and other archive material. Out of the 348 independent occurrences, landslides are the most represented category with 150 cases (43 % of the whole set of effects). The area, which is prone to slope instability even without seismic triggering, due to its lithological characters and rugged topography, undergoes now a much higher seismic risk because of the unconcerned strong urban development of recent decades. So, the obtained scenario of landslides distribution triggered by the 1908 earthquake helps to evaluate the impact on this region of a 1908-like future event.

Landslide Risk Assessment and Management Using IT Services and Tools: The EU BRISEIDE Project Approach

The increasing damage caused by natural hazards in the last decades in Europe, amplified by recent events including landslides (Messina, Sicily, September 2009), earthquakes (L’Aquila, Abruzzo, April 2009), forest fires (Greece, 2008) and floods (Central Europe) in the last years, points out the need for interoperable added-value services to support environmental safety and human protection. Many environmental analyses, e.g. monitoring seismic sequences, early warning systems for the evolution of intense rainstorms, the path of forest fires, cannot be performed without considering the evolution, over time, of geographic features. For this reason, providing access to harmonized data is only one of several steps towards delivering adequate support to risk assessment reduction and management. Scope of the present work is to present the implemented risk reduction and management pilots developed by BRISEIDE’s team project.