Publication Date:
2021-12-16
Description:
Sand boils, which are also known as sand blows or sand
volcanoes, are among the most common superficial effects
induced by high-magnitude earthquakes. These generally
occur in or close to alluvial plains when a strong earthquake
(M 〉5) strikes on a lens of saturated and unconsolidated
sand deposits that are constrained between silt-clay layers
[Ambraseys 1988, Carter and Seed 1988, Galli 2000, Tuttle
2001, Obermeier et al. 2005], where the sediments are converted
into a fluid suspension. The liquefaction phenomena
requires the presence of saturated and uncompacted sand,
and a groundwater table near the ground surface. This geological–
geomorphological setting is common and widespread
for the Po Plain (Italy) [Castiglioni et al. 1997]. The
Po Plain (ca. 46,000 km2) represents 15% of the Italian territory.
It hosts a population of about 20 million people
(mean density of 450 people/km2) and many infrastructures.
Thus, the Po Plain is an area of high vulnerability
when considering the liquefaction potential in the case of a
strong earthquake. Despite the potential, such phenomena
are rarely observed in northern Italy [Cavallin et al. 1977,
Galli 2000], because strong earthquakes are not frequent in
this region; e.g., historical data report soil liquefaction near
Ferrara in 1570 (M 5.3) and in Argenta 1624 (M 5.5) [Prestininzi
and Romeo 2000, Galli 2000]. In the Emilia quakes
of May 20 and 29, 2012, the most widespread coseismic effects
were soil liquefaction and ground cracks, which occurred
over wide areas in the Provinces of Modena, Ferrara,
Bologna, Reggio Emilia and Mantova (Figure 1). These were
the causes of considerable damage to buildings and the infrastructure.
The soil liquefaction and ground cracks were
accompanied by sand boils, which are described in this report.
The spatial distribution and geomorphological setting
of sand boils and ground cracks are also described here. A
detailed three-dimensional (3D) reconstruction of these features
is also presented, which was carried out using terrestrial
photogrammetry.
Since archeological times, fluvial ridges, and in general
sandy deposits on low plains have been the preferred sites for
human infrastructure, colonial houses, roads, etc. Therefore,
it is very important to understand how the local topography/
morphology interacts in the liquefaction processes. Numerous
distinctive seismic landforms were generated by the
May 2012 strong earthquakes (seven with M 〉5), and in particular,
sand boils and ground fractures. The sand-boil landforms,
also known as sand craters or sand volcanoes, are
formed by low mounds of sand that have been extruded
from fractures [Tuttle 2001]. The cone is a generally shortlived
structure that naturally collapses, starting from the center
holes that mark the water retreat back into the fracture.
Sand boils also occurred along larger cracks (with decimetric
lateral and vertical displacements). Here, the upper scarps
block the formation of craters and allow the deposition of a
sandy layer several centimeters thick (e.g. ca. 4 cm in the San
Carlo crack), on the lower side of the steep slope. These landforms
are highly vulnerable to erosion. After a few weeks,
they are washed out by rain, destroyed by human activity, or
masked by growing crops. Thus, ground surveys that investigate
these events have to be carried out as soon as possible
[Panizza et al. 1981]. In this report, we present preliminary
results using methods to map the detailed micro-morphology
of some representative liquefaction features (Figure 2)
that normally disappear for the aforementioned reasons, or
that are recorded only in qualitative terms.
Description:
Published
Description:
727-733
Description:
4.4. Scenari e mitigazione del rischio ambientale
Description:
JCR Journal
Description:
open
Keywords:
Sand boils, Digital elevation model, Liquefaction
;
04. Solid Earth::04.04. Geology::04.04.03. Geomorphology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink
