Some Interesting Results About Behaviour of Granular Media

This study represents an attempt to clarify some anomalous behaviour found in alluvional terrains when subjected to an earthquake. Our approach to the study of granular media has been bibliographic and experimental. Despite many studies carried on this topic, this behaviour is still little understood because of the complex nature of granular media. The goal to the experimental research was at least to confirm the „anomalous“ behaviour reported in previous studies (e.g., chain of force, not-uniform distribution of pressure, etc.). In particular, this study is focused on pressure distributions and their quantification with respect to the pure granular media, and especially refers to the behaviour of natural deposits, which are intermediate between granular and cohesive media

Seismic Site Effects in the Faulted Piancastagnaio Area (Italy): An Explanation Attempt

Analysis of seismic site effects is still an open issue within projects that deal with the reduction of seismic risk. In the absence of surface and borehole arrays measurements, the main methodological approach consists of the individuation and the consequent appraisal of the surface effects in presence of “an expected” earthquake, through integrated geological, geomorphological, geological-technical, geophysical multidisciplinary surveys and by the use of numerical modelling. In historically densely populated urban areas, it is possible to verify if the calculated accelerations can be, at least qualitatively, correlated to the level of damage to buildings. However, there are frequent cases in which meaningful incongruences between modelling results and macroseismic effects are found. In particular, this note shows the case of Piancastagnaio (Central Italy), a small town in which an earthquake occurred in 2000 with a local magnitude ML = 3.6. In some buildings, constructed in the 1920\u27s with earthquake-proof criteria for the times, this earthquake caused cracks justified only with intensities of VIII-IX degree of the EMS scale. The results of the analysis, carried out in compliance of the new Italian (D.M. dated 14.09.05, O.P.C.M. 3274 dated 20.03.03 and followings) and European (Eurocode8 dated 2003) seismic code and which classify the subsoil on the basis of the Vs30 values, do not justify such strong anomalous amplifications. With this work, the authors attempt an explanation of this kind of phenomenon and identify failure mechanisms as the cause of the identified local effects

Power-law frequency distribution of H/V spectral ratio of seismic signals: Evidence for a critical crust

We analyse records from several seismic stations in Central Italy (including some with multiple recording sites) for the statistical properties of spectra of both noise and earthquake signals. The main result is that the power-law scaling of most of the spectral H/V ratio statistical distributions leads to a so-called heavy tail. This is interpreted as a statistical distribution with a fractal dimension of about 2, which is almost certainly caused by a porous percolating medium beneath the stations due to some universal property of the crustal rocks crossed by the elastic waves propagation suggesting that the uppermost crust is in a critical state.Published49–543.1. Fisica dei terremotiJCR Journalrestricte

Shallow electrical and seismic imaging of the Pineto Mud Volcano (Central Italy)

Shallow underground electrical and seismic imaging was undertaken at the Pineto (Central Italy) Mud Volcano site using 2D-3D electrical resistivity tomography (ERT) and 2D reflection seismic surveys. This mud volcano or mud lump (known by the local population as “Cenerone Mud Volcano”) appears as a dome of about 15x10 m in size. The height is approximately 2 m with a crater 2.5 m of diameter where emission of fluids and solids (cold brine, mud, gas) occurs. Upper Pliocene-Lower Pleistocene foredeep pelitic deposits (clays with silty-sandy levels) overlain by clayey-silty deposits outcrop in the area. Below the Middle Pliocene deposits, a NNW-SSE anticline which runs approximately 2 kilometers to the WSW of the site represents the main element of the compressional tecnonic setting. Ditchs and streams in the area run along fault systems that are oriented NW-SE and NE-SW. These could be related to the upward migration of deep mud fluids. 2D-ERT results were used to determine the geometry of the high conductivity body related to the uprising of mud fluids and detecting changes in deposits. Detailed geometry reconstruction of the shallow upward migration of mud fluids was obtained by using 3D-ERT. A shear wave reflection seismic survey was undertaken to determine stratigraphic limits and to assess the occurrence of fractured zones along which mud fluids could migrate towards the surface. The survey results revealed that the uprising of deep fluids doesn’t occur exactly below the mud volcano at present. Instead, a high conductivity body occurs at approximately 60 m to the ENE, within a fractured zone in the undercompacted clays. The probable occurrence of a high permeability layer approximately between 20 m and 30 m below ground level, confined by clay layers, gives rise to an overpressured mud reservoir. This is the source of mud fluids which flow to the surface through a mud conduit that appears nearly horizontal at depth and then inclined towards the surface up to the mud volcano crater

Measurement of seismic local effects and 1D numerical modeling at selected sites affected by the 2009 seismic sequence of L’Aquila

Strong local effects occurred during the seismic sequence that affected the area of L’Aquila (Central Italy) in 2009, which culminated with a main shock of magnitude (Mw) 6.3 on the 6 April. Bearing in mind the magnitude, the vicinity of a regional capital to the epicentre, the presence of several historic centers and villages, which caused significant damage (IMCS max=9.5) and approximately 300 victims, among the main characteristics of this earthquake, was the variability of the recorded damages within the scale of 100 m in spite of the near field conditions and a distinct source mechanism. These local effects were measured with an array of geophones at selected sites near the city of L’Aquila. In one of the sites, located at Onna village which experienced maximum damage levels, the 1D numerical modeling allowed verifying the influence that the frequencey of the input motion has in the determination of superficial seismic effects. The numerical modeling, which was undertaken on the basis of the results from geomechanical, seismic and geoelectrical surveys, also allowed verifying that underestimation of local seismic amplification can be introduced by the current regulatory framework (Italian seismic regulatory guidance “Norme Tecniche per le Costruzioni” – D.M. of 14 January 2008) in contexts similar to that of L’Aquila

The 1930 earthquake and the town of Senigallia (Central Italy): an approach to seismic risk evaluation

The town of Senigallia is located on the Adriatic coast of the Marche and Romagna regions (Central Italy), an area affected by offshore seismicity. This city was almost completely destroyed by an earthquake of IX degree intensity on the Mercalli-Cancani-Sieberg scale (MCS) on October 30, 1930. This quake is the most recent and the best documented. In particular, this shock was characterized by strong differences in the damage levels at a scale of hundreds and tens of metres. The geographic position of Senigallia at the mouth of a river and its soil conditions, similar to many other coastal historical and tourist centres in the region, make this earthquake an important case history, useful for a better understanding of the seismic risk of the entire coastal area. This note reports the first results of a study on the possible causes of the different damage levels. The research started with the history and town-planning evolution of Senigallia, then. the regional or local geological characteristics were considered by geological, geotechnical and geophysical investigations