Renewal models of seismic recurrence applied to paleoseismological data

Because paleoseismology can extend the record of earthquakes back in time up to several millennia, it represents a great opportunity to study how earthquakes recur through time and thus provide innovative contributions to seismic hazard assessment. A worldwide compilation of a database of recurrence from paleoseismology was developed in the frame of the ILP project “Earthquake Recurrence Through Time”, from which we were able to extract five sequences with 6 and up to 9 dated events on a single fault. By using the age of the paleoearthquakes with their associated uncertainty we have tested the null hypothesis that the observed inter-event times come from a uniform random distribution (Poisson model). We have made use of the concept of likelihood for a specific sequence of observed events under a given occurrence model. The difference dlnL of the likelihoods estimated under two hypotheses gives an indication of which between the two hypotheses fits better the observations. To take into account the uncertainties associated to paleoseismological data, we used a Monte Carlo procedure, computing the average and the standard deviation of dlnL for 1000 inter-event sets randomly obtained by choosing the occurrence time of each event within the limits of uncertainty provided by the observations. Still applying a Monte Carlo procedure, we have estimated the probability that a value equal to or larger than each of the observed dlnLs comes by chance from a Poisson distribution of inter-event times. These tests have been carried out for a set of the most popular statistical models applied in seismic hazard assessment, i.e. the Log-normal, Gamma, Weibull and Brownian Passage Time (BPT) distributions. In the particular case of the BPT distribution, we have also shown that the limited number of dated events creates a trend to reducing both the observed mean recurrence time and the coefficient of variation for the studied sequence which can possibly bias the results. Our results show that a renewal model, associated with a time dependent hazard, and some kind of predictability of the next large earthquake on a fault, only for the Fucino site, out of the five sites examined in this study, is significantly better than a plain time independent Poisson model. The lack of regularity in the earthquake occurrence for three of the examined faults can be explained either by the large uncertainties in the estimate of paleoseismological occurrence times or by physical interaction between neighbouring faults

Probabilistic approach to earthquake prediction.

The evaluation of any earthquake forecast hypothesis requires the application of rigorous statistical methods. It implies a univocal definition of the model characterising the concerned anomaly or precursor, so as it can be objectively recognised in any circumstance and by any observer.A valid forecast hypothesis is expected to maximise successes and minimise false alarms. The probability gain associated to a precursor is also a popular way to estimate the quality of the predictions based on such precursor. Some scientists make use of a statistical approach based on the computation of the likelihood of an observed realisation of seismic events, and on the comparison of the likelihood obtained under different hypotheses. This method can be extended to algorithms that allow the computation of the density distribution of the conditional probability of earthquake occurrence in space, time and magnitude. Whatever method is chosen for building up a new hypothesis, the final assessment of its validity should be carried out by a test on a new and independent set of observations. The implementation of this test could, however, be problematic for seismicity characterised by long-term recurrence intervals. Even using the historical record, that may span time windows extremely variable between a few centuries to a few millennia, we have a low probability to catch more than one or two events on the same fault. Extending the record of earthquakes of the past back in time up to several millennia, paleoseismology represents a great opportunity to study how earthquakes recur through time and thus provide innovative contributions to time-dependent seismic hazard assessment. Sets of paleoseimologically dated earthquakes have been established for some faults in the Mediterranean area: the Irpinia fault in Southern Italy, the Fucino fault in Central Italy, the El Asnam fault in Algeria and the Skinos fault in Central Greece. By using the age of the paleoearthquakes with their associated uncertainty we have computed, through a Montecarlo procedure, the probability that the observed inter-event times come from a uniform random distribution (null hypothesis). This probability is estimated approximately equal to 8.4% for the Irpinia fault, 0.5% for the Fucino fault, 49% for the El Asnam fault and 42% for the Skinos fault. So, the null Poisson hypothesis can be rejected with a confidence level of 99.5% for the Fucino fault, but it can be rejected only with a confidence level between 90% and 95% for the Irpinia fault, while it cannot be rejected for the other two cases. As discussed in the last section of this paper, whatever the scientific value of any prediction hypothesis, it should be considered effective only after evaluation of the balance between the costs and benefits introduced by its practical implementation

Bringing Earth into the scene of a primary school: a science theatre experiment

Studies have shown that narrative is a valid tool to transmit science in a school context (Negrete&Lartigue 2010). We explored science theatre to promote earthquake knowledge and risk preparedness by readapting an old legend describing the 1908 Messina earthquake into a script, which was then performed in a primary school. We evaluated the experience by designing a questionnaire inspired by the Düss Fairy Tales method and a semi-structured questionnaire. Preliminary results strongly encourage science theatre as a mean to transfer knowledge and opens new opportunities to use this method as an agent of change in behaviour before and during an earthquake

Investigation of the active Celano-L'Aquila fault system, Abruzzi (central Apennines, Italy) with combined ground-penetrating radar and palaeoseismic trenching

n/

ScienzAperta, an outreach week about Earth Science at INGV

Scientific exhibitions, hands-on laboratories for kids, meetings and seminars with researchers, guided tours to laboratories are the ingredients for the outreach week "ScienzAperta" at Istituto Nazionale di Geofisica e Vulcanologia (INGV). ScienzAperta, the Open Science Week, responds to the needs and the request of the society for more information on issues regarding our Planet. The common goal is to engage INGV researchers to be involved in a correct, straightforward and efficient communication to public about research and technological innovations they perform. In a world that request citizens to be more informed, aware and able to make crucial decisions about their own health and safety, the knowledge is crucial to handle doubts and to know how to choose with consciousness. Since 2011, ScienzAperta held once per year during spring; several INGV headquaters over the Italian territory open their doors to public. The goal is to help raise awareness about earth sciences, and research activities at INGV, as well as intrigue, interest, and stimulate audiences of all ages. Researchers and technicians involved in outreach activities conceive scientific programs to present research as the heritage of all. Some activities were organized in collaboration with other institutions and with transdisciplinary approaches. For example in 2011 edition, in collaboration with Istituto Nazionale di Ricerca per gli Alimenti (INRAN), geophysics and nutrition sciences were linked through geodynamic evolution and diet evolution of the Mediterranean. In all the past three editions music-based initiatives were designed to attract young people as well as generic public, such as the performances "seismic waves, sound waves, from earthquake to music", "musical journey of Italian earthquakes", "waves, sympathy and music", "landscapes, territory and wines". The ScienzAperta programs were designed giving special attention to pupils and teachers. Hand-on laboratories for kids on earthquakes, volcanoes, and also on INGV researches in Antarctica were organized, and achieved great participation and appreciation. Analysis of questionnaires distributed among adult visitors and children during an Open Saturday in 2013 in Rome provided hints to improve the outreach event format. Acquired pieces of information were perceived as useful to get more in depth with the topics by mostly all adult visitors; nothing was perceived as not clear, appreciation comments came as well as invitations to repeat such events more frequently; children perceived the games as very interesting, very useful and well organized, but in some cases the notions not so easy to be understood

Tephrochronology in faulted Middle Pleistocene tephra layer in the Val d’Agri area (Southern Italy)

The High Agri River Valley is a Quaternary Basin located along the hinge of the Southern Apennines fold-andthrust belt. The inner margin of the orogen has been affected by intense transtensional and normal faulting, which accompanied vigorous volcanism during the Quaternary. Marker tephra layers are distributed across the whole of Southern Italy and provide a powerful tool to constrain both the size of eruptions and the regional activity of extensional faults controlling basin evolution. Paleoseismological trenching within the Monti della Maddalena range, that borders the Agri River Valley to the south-west, has exposed a faulted stratigraphic sequence and recovered a 10 cm thick tephra layer involved in deformation. This is the first tephra horizon recognized in the high Agri Valley, which, based on the stratigraphic study of the trench, lies in a primary position. 40Ar/39Ar dating constrain its age to 266 ka and provide an important marker for the Middle Pleistocene tephrochronology of the region. Together with dating, geochemical analysis suggests a possible volcanic source in the Campanian region

Paleoearthquakes of the Düzce fault (North Anatolian Fault Zone): insights for earthquake recurrence

The November 12, 1999, Mw 7.1 earthquake, ruptured the Düzce segment of the North Anatolian Fault Zone and produced a ca. 40 km-long surface rupture. To improve knowledge about earthquake recurrence on this fault, we undertook paleoseismological trench investigations. We found evidence for repeated surface faulting paleoearthquakes pre-dating the 1999 event during the past millennium. Dating was based on radiocarbon, 210Pb analyses, and archaeological considerations. In addition to the 1999 earthquake, prior surface faulting earthquakes are dated as follows: AD1685-1900 (possibly end of 19th century); AD1495-1700; AD685-1020 (possibly AD890-1020). The AD967 and AD1878 historical earthquakes are good candidates to have ruptured the Düzce fault correlating with the oldest and penultimate paleoearthquakes. No obvious correlation for the third paleoearthquake (AD1495-1700) exists. These results shows that the Düzce fault considerably participates, along with the parallel Mudurnu fault sections, in the seismogenic deformation taking place along this part of the North Anatolian Fault. Four events since AD 685-1020 (possibly AD890-1020), would yield an average recurrence time for the Düzce fault of 330-430 yr (possibly 330-370 yr). The three most recent earthquakes, including 1999, occurred within 500 yr. Merging results from other paleoseismological studies along the Düzce fault show a consistency of results and yields average recurrence times for the past 2000 yr of 320-390 yr. Assuming that the 1999 slip (2.7 m average, 5 m maximum) is representative of the behavior of this fault, the above recurrence times yield a reference figure of fault slip rate in the range 6.9-15.6 mm/yr

Paleoearthquakes of the Düzce fault (North Anatolian Fault Zone): implications for earthquake recurrence

The November 12, 1999, Mw 7.1 earthquake, ruptured the Düzce segment of the North Anatolian Fault Zone and produced ca. 40 km-long surface ruptures. To learn about recurrence of large surface faulting earthquakes on this fault, we undertook paleoseismological trench investigations. We found evidence for repeated surface faulting paleoearthquakes pre-dating the 1999 event. Dating was based on radiocarbon and 210Pb analyses as well as on archaeological considerations. By merging information obtained from all the trenches we reconstructed the seismic history of the Düzce fault for the past millennium. We correlated coeval events between different trench sites under the assumption that, similarly to the 1999 event, paleoearthquakes ruptured the whole Düzce fault. Besides the 1999 earthquake, prior surface faulting earthquakes are dated as follows: AD1685-1900 (possibly end of 19th century); AD1685-1900 (possibly close to AD 1700); AD1185-1640; AD685-1220 (possibly AD800-1000). Thus, the AD1719, AD1878 and AD1894 historical earthquakes, may have ruptured the Düzce fault and not the faults they are usually associated to or, alternatively, a cascade of events occurred on the Düzce and nearby faults (similarly to the Izmit and Düzce 1999 earthquakes). Five events since AD 685-1220 (possibly AD800-1000), would yield an average recurrence time for the Düzce fault, of 200-325 yr (possibly 250-300 yr). The three most recent earthquakes, including 1999, occurred within 300 yr and may be suggestive of clustering. Assuming that the average 1999 slip is characteristic for this fault, the above recurrence times yield slip rates of 6.7-13.5 mm/yr

Detecting young, slow‐slipping active faults by geologic and multidisciplinary high‐resolution geophysical investigations: A case study from the Apennine seismic belt, Italy.

The Southern Apennines range of Italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics, coupled to very recent (Middle Pleistocene) onset and slow slip rates of active normal faults. As shown by the Irpinia Fault, source of a M6.9 earthquake in 1980, major faults might have small cumulative deformation and subtle geomorphic expression. A multidisciplinary study including morphological-tectonic, paleoseismological, and geophysical investigations has been carried out across the extensional Monte Aquila Fault, a poorly known structure that, similarly to the Irpinia Fault, runs across a ridge and is weakly expressed at the surface by small scarps/warps. The joint application of shallow reflection profiling, seismic and electrical resistivity tomography, and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions. Geophysical data clearly (1) image a fault zone beneath suspected warps, (2) constrain the cumulative vertical slip to only 25–30 m, (3) delineate colluvial packages suggesting coseismic surface faulting episodes. Paleoseismological investigations document at least three deformation events during the very Late Pleistocene (<20 ka) and Holocene. The clue to surface-rupturing episodes, together with the fault dimension inferred by geological mapping and microseismicity distribution, suggest a seismogenic potential of M6.3. Our study provides the second documentation of a major active fault in southern Italy that, as the Irpinia Fault, does not bound a large intermontane basin, but it is nested within the mountain range, weakly modifying the landscape. This demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region. More in general, our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques. The proposed multidisciplinary methodology can be effective in regions characterized by young and/or slow slipping active faults.PublishedB113073.2. Tettonica attivaJCR Journalpartially_ope

Evidence for surface rupture associated with the Mw 6.3 L’Aquila earthquake sequence of April 2009 (central Italy)

An earthquake of Mw = 6.3 struck L Aquila town (central Italy) on 6 April 2009 rupturing an ~18-km-long SW-dipping normal fault. The aftershock area extended for a length of more than 35 km and included major aftershocks on 7 and 9 April and thousands of minor events. Surface faulting occurred along the SW-dipping Paganica fault with a continuous extent of ~2.5 km. Ruptures consist of open cracks and vertical dislocations or warps (0.1m maximum throw) with an orientation of N130°–140°. Small triggered slip and shaking effects also took place along nearby synthetic and antithetic normal faults. The observed limited extent and small surface displacement of the Paganica ruptures with respect to the height of the fault scarps and vertical throws of palaeo-earthquakes along faults in the area put the faulting associated with the L' Aquila earthquake in perspective with respect to the maximum expected magnitude and the regional seismic hazard.Published43-513.2. Tettonica attivaJCR Journalreserve