Publication Date:
2020-02-24
Description:
Large earthquakes that have occurred in recent years in densely populated areas of the world
(e.g. Izmit, Turkey, 17 August 1999; Duzce, Turkey, 12 November 1999; Chi-Chi, Taiwan 20
September 1999, Bhuj, India, 26 January 2001; Sumatra 26 December 2004; Wenchuan, China,
May 12, 2008; L’Aquila, Italy, April 6, 2009; Haiti, January 2010 Turkey 2011) have dramatically
highlighted the inadequacy of a massive portion of the buildings erected in and around the
epicentral areas. For example, the Izmit event was particularly destructive because a large
number of buildings were unable to withstand even moderate levels of ground shaking,
demonstrating poor construction criteria and, more generally, the inadequacy of the
application of building codes for the region. During the L’Aquila earthquake (April, 06, 2009;
Mw=6.3) about 300 persons were killed and over 65,000 were left homeless (Akinci and
Malagnini, 2009). It was the deadliest Italian earthquake since the 1980, Irpinia earthquake, and
initial estimates place the total economic loss at over several billion Euros. Many studies have
already been carried out describing the rupture process and the characteristics of local site
effects for this earthquake (e.g. D’Amico et al., 2010a; Akinci et al., 2010). It has been observed
that many houses were unable to withstand the ground shaking.
Building earthquake-resistant structures and retrofitting old buildings on a national scale may
be extremely costly and may represent an economic challenge even for developed western
countries, but it is still a very important issue (Rapolla et al., 2008). Planning and design should
be based on available national hazard maps, which, in turn, must be produced after a careful
calibration of ground motion predictive relationships (Kramer, 1996) for the region.
Consequently, the assessment of seismic hazard is probably the most important contribution
of seismology to society. The prediction of the earthquake ground motion has always been
of primary interest for seismologists and structural engineers. For engineering purposes it is
necessary to describe the ground motion according to certain number of ground motion
parameters such as: amplitude, frequency content and duration of the motion. However it is
necessary to use more than one of these parameters to adequately characterize a particular
ground motion.
Updating existing hazard maps represents one of the highest priorities for seismologists,
who contribute by recomputing the ground motion and reducing the related uncertainties.
The quantitative estimate of the ground motion is usually obtained through the use of the so-called predictive relationships (Kramer, 1996), which allow the computation of specific
ground-motion parameter as a function of magnitude, distance from the source, and
frequency and they should be calibrated in the region of interest. However this is only
possible if seismic records of large earthquakes are available for the specific region in order
to derive a valid attenuation relationship regressing a large number of strong-motion data
(e.g. Campbell and Bozorgnia, 1994; Boore et al., 1993; Ambraseys et al., 1996, Ambraseys
and Simpson, 1996; Sabetta and Pugliese, 1987, 1996; Akkar and Bommer 2010). For the
Italian region the most used attenuation relationships are those obtained by Sabetta and
Pugliese (1987, 1996) regressing a few data recorded for earthquakes in different tectonic
and geological environments. It has been shown in several cases that it is often not adequate to
reproduce the ground motion in each region of the country using a single model. Furthermore
the different crustal properties from region to region play a key role in this kind of studies.
However, the attenuation properties of the crust can be evaluated using the background
seismicity as suggested by Chouet et al. (1978) and later demonstrated by Raoff et al. (1999)
and Malagnini et al (2000a, 2007). In other words, it becomes possible to develop regionallycalibrated
attenuation relationships even where strong-motion data are not available. One of
the purposes of this work is to describe quantitatively the regional attenuation and source
characteristics for constraining the amplitude of strong motion expected from future
earthquakes in the area. In this work we describe how to use the background seismicity to
perform the analysis (details in Malagnini et. 2000a, 2007). In particular, this chapter describes
the procedures and techniques to study the ground motion and will focus on describing both
strong motion attenuation relationships and the techniques used to derive the ground motion
parameters even when strong ground motion data are not available. We will present the
results obtained for different regions of the Italian peninsula, showing that the attenuation
property of the crust and of the source can significantly influence the ground motion. In
addition, we will show that stochastic finite-fault modeling based on a dynamic frequency
approach, coupled with field investigations, confirms to be a reliable and practical method to
simulate ground motion records of moderate and large earthquakes especially in regions
prone to widespread structural damage.
Description:
Published
Description:
69-85
Description:
open
Keywords:
ground motions
;
04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
book chapter
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