Seismic Microzonation

In Umbria various seismic microzonation actions have been done over 38 years at the turn of 2 millennia. The evolutionary path made since 1980 was important and was as follows.
1980-For the first time, different areas of the territory were identified, to which attention should be paid to the reconstruction of the buildings.
1997-For the first time different categories of hazard were defined that could overlap each other identifying homogeneous areas.
1998-For the first time, geognostic and geophysical surveys, numerical modeling, and any area susceptible to seismic amplification were associated with an amplification factor (FA) that was used for the reconstruction according to the specific legislation that was adopted.
1998-For the first time, instrumental seismic microzonation investigations and detailed geognostic and geophysical surveys have been carried out, providing technical data to be used in the design field.
1999-For the first time, an entire Italian regional territory had knowledge about susceptibility to local seismic amplification.
2000-For the first time, seismic microzonation surveys have been carried out by simultaneously applying instrumental analyzes and numerical analyzes for the same areas, borrowing the different results obtained to be used in the design field.
2006-2013-For the first time we have defined:
• areas with homogeneous seismic behavior after having carried out extremely detailed surveys.
• acceleration response spectra and amplification factors for different periods intervals.
• the areas of applicability of the individual response spectra.
• response spectra for strategic buildings and major relevant buildings.
2008-For the first time, the zones of respect for active (and capable) fault were indicated as standard.
2014-For the first time it has been applied at national level:
• A multi-annual national survey of seismic microzonations and analysis for the limit condition.
• unequivocal national standards and guidelines.
• a control by an inter-institutional Technical Commission that has played and plays a fundamental role in monitoring the activities of seismic micro-zoning and the emergency limit condition, also providing essential contributions to support the same activities through the drafting of addresses, lines guide, reference standard.
2018-For the first time:
• detailed seismic microzonation investigations were carried out at the same time in a very large number of municipalities of 4 regions, according to timelines and uniform procedures in a short time.
• general criteria have been defined and approved for the use of the results of the level 3 seismic microzonation studies for the reconstruction in the territories affected by the seismic events.
Not all actions have completely reached the conclusion and others are underway. We have moved from a degree of qualitative knowledge to an ever-increasing amount of detail. All the results have been made available online, even when possible, as open data and this has greatly facilitated the application of the results also because the Umbria Region has made their use mandatory.
In conclusion, the execution of studies and applications of the achieved knowledge applied to the reconstruction has allowed to decrease from 1 to 3 degrees the macroseismic intensity.

In Umbria various seismic microzonation actions have been done over 38 years at the turn of 2 millennia. The evolutionary path made since 1980 was important and was as follows.
1980-For the first time, different areas of the territory were identified, to which attention should be paid to the reconstruction of the buildings.
1997-For the first time different categories of hazard were defined that could overlap each other identifying homogeneous areas.
1998-For the first time, geognostic and geophysical surveys, numerical modeling, and any area susceptible to seismic amplification were associated with an amplification factor (FA) that was used for the reconstruction according to the specific legislation that was adopted.
1998-For the first time, instrumental seismic microzonation investigations and detailed geognostic and geophysical surveys have been carried out, providing technical data to be used in the design field.
1999-For the first time, an entire Italian regional territory had knowledge about susceptibility to local seismic amplification.
2000-For the first time, seismic microzonation surveys have been carried out by simultaneously applying instrumental analyzes and numerical analyzes for the same areas, borrowing the different results obtained to be used in the design field.
2006-2013-For the first time we have defined:
• areas with homogeneous seismic behavior after having carried out extremely detailed surveys.
• acceleration response spectra and amplification factors for different periods intervals.
• the areas of applicability of the individual response spectra.
• response spectra for strategic buildings and major relevant buildings.
2008-For the first time, the zones of respect for active (and capable) fault were indicated as standard.
2014-For the first time it has been applied at national level:
• A multi-annual national survey of seismic microzonations and analysis for the limit condition.
• unequivocal national standards and guidelines.
• a control by an inter-institutional Technical Commission that has played and plays a fundamental role in monitoring the activities of seismic micro-zoning and the emergency limit condition, also providing essential contributions to support the same activities through the drafting of addresses, lines guide, reference standard.
2018-For the first time:
• detailed seismic microzonation investigations were carried out at the same time in a very large number of municipalities of 4 regions, according to timelines and uniform procedures in a short time.
• general criteria have been defined and approved for the use of the results of the level 3 seismic microzonation studies for the reconstruction in the territories affected by the seismic events.
Not all actions have completely reached the conclusion and others are underway. We have moved from a degree of qualitative knowledge to an ever-increasing amount of detail. All the results have been made available online, even when possible, as open data and this has greatly facilitated the application of the results also because the Umbria Region has made their use mandatory.
In conclusion, the execution of studies and applications of the achieved knowledge applied to the reconstruction has allowed to decrease from 1 to 3 degrees the macroseismic intensity.

The HVSR method applied to seismic noise can be a very useful technique to map the site effects of the territory, to identify the thickness
of the soft covering and so the depth of the seismic bedrock. The case of the urban area of Oliveri is presented. Because of its high seismic
hazard this area has been subject of first level seismic microzonation. The town lies on a large coastal plain made of mixed fluvial/marine
sediments, overlapping a deformed substrate. In order to identify points on the area probably suffering of relevant site effects and to define
a preliminary Vs subsurface model, 23 HVSR measurements were performed. A clustering technique of continuous signals has been used to
optimize the calculation of the HVSR curves and 42 reliable peaks, in the frequency range 0.1-20 Hz, have been identified. A second clustering
technique has been applied to the set of 42 vectors, containing coordinates, frequency and amplitude of each peak, to identify subsets
attributed to the same seismic discontinuities. Three main clusters have been identified. The two characterized by lower frequencies have
been considered in the HVSR data inversion, as stratigraphic peaks probably caused by the seismic bedrock. Finally, the morphology of the
top of the seismic bedrock has been mapped. The deepening of the seismic bedrock below the mouth of the Elicona Torrent suggests the possible
presence of a buried paleo-valley.

The so called “valley effect” relates to the typical seismic  response of basin shaped bedrock filled by quaternary sediments. It is an aspect of the renown “local seismic effect” that shall be taken into account when dealing with microzoning studies. Several experimental surveys and numerical simulations performed worldwide over the last 40 years, confirmed that valley responses under seismic excitations show common features in various geological contexts as far as the sedimentary valleys (e.g. alluvial and lacustrine plains), the intermountain valleys (e.g. alpine valleys) and graben shaped basins. Such features mainly depend on the basin geometry, referred to as the shape ratio SR, and the sediment and basin impedance contrast IC. Although researchers agree on the prominent role of local seismic effects for interpreting erratic damages caused by seismic shaking in urbanized areas, no fully shared strategies have been identified for taking into account valley effect within microzoning studies.
In this paper, a numerical simulations on three models of trapezoidal shaped basins have been performed. These valley models relate to sediments and basins detected within the Tuscany Region territory during the VEL project. Results, in terms of the amplification index FA have been provided. Three “valley effect charts” for various SR and IC values have been propose for taking into account the local seismic effects due to the basin amplifications within microzoning maps.

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M W 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain.

A B S T R A C T In this work, we analyze the macroseismic fields of the main historical earthquakes occurred in western Liguria (northwestern Italy) in order to identify possible relations between the isoseismal patterns and the local geological setting. Anomalies in the spatial distribution of macroseismic intensities are often attributed to site effects. We observed that, in the region of study, such anomalies are mainly located in areas characterized by outcropping Pliocene soil deposits, mainly made up of stiff silty and marly clays. To investigate the influence of such deposits on ground response, both horizontal-to-vertical spectral ratio measurements and numerical site response analyses were carried out. For all sites analyzed, the spectral ratio curves show marked amplification peaks between 2 and 5 Hz. Following such empirical evidence, equivalent linear ground response analyses were performed in order to examine the relation between the measured resonance frequencies and the response of a set of soil columns presenting Pliocene marly-clayey deposits at their top. To this end, a database of geotechnical and geophysical properties, including > 50 reference soil profiles, was compiled. This database was used to define alternative numerical models considering three different ranges of thickness of the Pliocene marly-clayey deposits (between 5 and 35 m, 30 and 65 m, 60 and 105 m). Results show marked amplification effects in the ranges 1–3 Hz, 2–5 Hz, and 3–10 Hz depending on the thickness of the investigated soil deposits. These frequency ranges are in agreement with those observed from the experimental measurements, which are therefore proved adequately representative of the resonance frequencies of the Pliocene marly-clayey deposits. Therefore, based on our findings, such deposits can be considered an essential factor in producing the " anomalies " observed in the isoseismal patterns of the macroseismic fields of the historical earthquakes occurred in western Liguria.

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M W 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain.

The earthquake record and the Code for design and construction in seismic regions in Bulgaria have shown that the territory of the Republic of Bulgaria is exposed to a high seismic risk due to local shallow and regional strong intermediate-depth seismic sources. The available strong motion database is quite limited, and therefore not representative at all of the real hazard. The application of the neo-deterministic seismic hazard assessment procedure for two main Bulgarian cities has been capable to supply a significant database of synthetic strong motions for the target sites, applicable for earthquake engineering purposes. The main advantage of the applied deterministic procedure is the possibility to take simultaneously and correctly into consideration the contribution to the earthquake ground motion at the target sites of the seismic source and of the seismic wave propagation in the crossed media. We discuss in this study the result of some recent applications of the neo-determi...

La disponibilidad de modelos y técnicas de cálculo más refinadas para la evaluación de la amenaza sísmica, así como la existencia de una mayor cantidad de registros de eventos sísmicos, permite realizar una actualización de los estudios de amenaza sísmica a nivel nacional. Este artículo describe la nueva metodología utilizada para estimar diferentes intensidades sísmicas esperadas para diseño y construcción de edificaciones sismorresistentes en el territorio colombiano. Se presentan los resultados de intensidad obtenidos para diferentes períodos de retorno y ordenadas espectrales para edificaciones de diferentes períodos estructurales, los cuales, además de servir para establecer los valores de diseño en las nuevas Normas NSR-10, también son un insumo necesario para la realización de estudios de microzonificación y de riesgo sísmico dentro del territorio nacional de la República de Colombia./ The use of more refined models and computational techniques for seismic hazard evaluation a...

Experience from past earthquakes has demonstrated the vulnerability of structures to seismically induced ground deformation. During earthquake, soil can fail due to liquefaction with devastating effect such as landslides, lateral spreading, or large ground settlement. The phenomenon of liquefaction of soil had been observed for many years, but was brought to the attention of engineers after Niigata (1964) Alaska earthquakes (1964). Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world (Borcherdt R.D 1991; Dobry R, 1981). During the Bhuj earthquake, India on 26th January 2001 (M=7.7) lot of damages had been occurred due to liquefaction and other ground failures (Rao and Mohanty, 2001). In this paper, a preliminary liquefaction hazard assessment was carried out using the available SPT data. From these investigations it was observed that a vast majority of liquefaction occurrences were associated with sandy soils and silty clays of low plasticity.

Abstract The seismic vulnerability of Kashmir basin is evident from the historical and instrumental earthquake records in general and the capital city of Srinagar in particular. An attempt is made here to deliver the seismic microzonation map of this scenic city. To do so, probabilistic and geotechnical hazard representing the primary seismic hazard, secondary seismic hazard and site conditions are used as input themes. The themes considered for the holistic integrated hazard quantification are the peak ground acceleration at engineering bedrock, shear wave velocity distribution representing site conditions, liquefaction potential index, site amplification ratio and predominant frequency distribution. All these themes have been assigned appropriate weights and their features. The highest weight was given to peak ground acceleration, followed by shear wave velocity distribution, liquefaction potential index, site amplification ratio and predominant frequency themes. These weighted themes are then integrated in the GIS environment to generate seismic microzonation map of the Srinagar city. This map is expressed in terms of the Seismic Hazard Index (SHI) and is accordingly grouped into two classes: very high and severe. The results demonstrate that Srinagar city is susceptible to very high seismic hazard, especially when predicted peak ground acceleration is of the order of 0.605–0.63 g at the bedrock.

Experience from past earthquakes has demonstrated the vulnerability of structures to seismically induced ground deformation. During earthquake, soil can fail due to liquefaction with devastating effect such as landslides, lateral spreading, or large ground settlement. The phenomenon of liquefaction of soil had been observed for many years, but was brought to the attention of engineers after Niigata (1964) Alaska earthquakes (1964). Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world (Borcherdt R.D 1991; Dobry R, 1981). During the Bhuj earthquake, India on 26th January 2001 (M=7.7) lot of damages had been occurred due to liquefaction and other ground failures (Rao and Mohanty, 2001). In this paper, a preliminary liquefaction hazard assessment was carried out using the availa...

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M W 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain.

Abstract In this work, we analyze the macroseismic fields of the main historical earthquakes occurred in western Liguria (northwestern Italy) in order to identify possible relations between the isoseismal patterns and the local geological setting. Anomalies in the spatial distribution of macroseismic intensities are often attributed to site effects. We observed that, in the region of study, such anomalies are mainly located in areas characterized by outcropping Pliocene soil deposits, mainly made up of stiff silty and marly clays. To investigate the influence of such deposits on ground response, both horizontal-to-vertical spectral ratio measurements and numerical site response analyses were carried out. For all sites analyzed, the spectral ratio curves show marked amplification peaks between 2 and 5 Hz. Following such empirical evidence, equivalent linear ground response analyses were performed in order to examine the relation between the measured resonance frequencies and the response of a set of soil columns presenting Pliocene marly-clayey deposits at their top. To this end, a database of geotechnical and geophysical properties, including > 50 reference soil profiles, was compiled. This database was used to define alternative numerical models considering three different ranges of thickness of the Pliocene marly-clayey deposits (between 5 and 35 m, 30 and 65 m, 60 and 105 m). Results show marked amplification effects in the ranges 1–3 Hz, 2–5 Hz, and 3–10 Hz depending on the thickness of the investigated soil deposits. These frequency ranges are in agreement with those observed from the experimental measurements, which are therefore proved adequately representative of the resonance frequencies of the Pliocene marly-clayey deposits. Therefore, based on our findings, such deposits can be considered an essential factor in producing the “anomalies” observed in the isoseismal patterns of the macroseismic fields of the historical earthquakes occurred in western Liguria.

A microzonation study for an industrial area located in Sicily (southern Italy) has been carried out through an integrated approach using GIS and modelling tools for subsurface geology, together with procedures for soil response estimation. The seismic input was provided by an updated seismic hazard analysis aimed at better defining and characterizing the seismogenic sources active in the region. The approach involved the development of a model of the subsurface geology through the interpretation of several borehole data coming from industrial or private wells records. The lithologies described in the borehole logs were reclassified according to main litotechnical units for which seismological properties were available from previous studies. The reclassified logs were then interpreted using the GSI3D software (Geological Surveying and Investigation in 3 Dimensions), which allows to draw and cross-correlate geological sections over the whole study area, to produce 3D surfaces which m...

The 2006 Yogyakarta earthquake caused an extensive damage to various areas of Yogyakarta regions. The damage distribution indicates the role of local site effects during the earthquake as the damage extended from Bantul Regency in Yogyakarta Province to Klaten Regency in Central Java. Microzonation based on the damage distribution is then carried out using Horizontal-to-Vertical Spectral Ratio (HVSR) technique. From this technique, amplification factor and predominant frequency can be obtained and then spatially mapped. Inversion can also be conducted to the HVSR curves to infer the geological condition of the study area.

The investigation of the site-effects using spectral ratio methods in the city of Timisoara is presented. A non-reference-site technique, often called Nakamura's method is used to determine the resonance frequencies, fr, of the uppermost sedimentary layers. The method was applied on i) seismic noise time-series (HVSRN); ii) earthquakes waveforms recorded by Timisoara Seismic Station (TIM). The resonance frequencies and H/V ratios amplitudes were mapped for a first- order evaluation of site response and to emphasize lateral variations of the seismic ground motion as a microzonation main step. These frequencies were also correlated with the local geology, the observed macroseismic intensities in the city and with the theoretical fundamental frequencies of the buildings.