Seismic hazard assessment accounting for earthquake-induced phenomena

through spatial multi-criteria analysis in Xerias torrent basin, Greece

The present study focuses on the area of the Xerias torrent drainage basin, located at

Northeastern Peloponnese, Greece. The study area is situated at the eastern part of the Gulf of

Corinth, an active tectonic rift, characterized by high seismic activity and intense extension

which is accommodated by a series of major active normal faults. As a result, it has frequently

suffered damage from earthquakes which in some cases were accompanied by seismically-

induced phenomena. These secondary phenomena include landslides and soil liquefaction and

in some cases have the potential to cause more damage and casualties than the earthquake

itself. Classic deterministic and probabilistic approaches of seismic hazard assessment do not

account for seismically-induced phenomena and accordingly such analyses overlook locations

prone to these secondary effects. The aim of our research is to evaluate seismic hazard not

only as the hazard associated with the occurrence of potential earthquakes in the particular

area, but also assess areas exposed to slope destabilization phenomena and soil liquefaction

under seismic shaking. For this purpose we will use the pure statistical and the semi-statistical

seismic hazard approaches along with the Analytic Hierarchy Process (AHP) to estimate the

susceptibility of the study area to earthquakes and their triggering effects. AHP is a multi-

criteria decision making method that helps to deal with a complex problem taking into

account multiple conflicting criteria. The extent of the study area is limited, so classic

probabilistic seismic hazard assessment yields a uniform seismic hazard throughout the study

area. Afterwards, we evaluated separately the hazard from seismically-induced landslides and

soil liquefaction and subsequently we stacked them into one single hazard map reflecting the

hazard due to seismically-induced phenomena. Such map complement the standard PSHA

maps and highlight areas that need special attention by planners and authorities so as to

mitigate not only the consequences of earthquakes but also their secondary effects.

Figure 1. The digital elevation model (DEM) of the Xerias drainage basin superimposed by

the Xerias torrent, the main towns and the. The red rectangle in the inset highlights the

location of the study area within the Greek territory.

Figure 2. Map of the study area showing local active and probable active faults (E.P.P.O.

Neotektonic map “Korinthos” sheet 1:100.000) along with the epicenters of historical and

instrumentally recorded major earthquakes (Ms>6.0) (Ambraseys & Jackson 1990, 1997;

Papazachos & Papazachou 2003).

Calculate the Hazard of the study

area

Hazard 1 earthquake

triggered landslide

Slope

0-5

5-12

12-18

18-25

25-35

>35

Geology

Recent deposits

Neogene formations

Shales-chert formation

Carbonate rocks

Arias intensity

Spi20

Flat slope

Lower slope

Valley

Middle slope

Upper slope

Ridge

Distance to fault (m)

0-50

50-100

100-150

150-200

>200

Distance to road (m)

0-50

50-100

100-150

150-200

>200

Distance to stream (m)

0-50

50-100

100-150

150-200

>200

Aspect

Flat

North

NE

East

SE

South

SW

West

NW

Land use

Burnt area

Mine

Agricultural Land

Bush

Forest

Urban

AHP

Hazard 2 earthquake

triggered liquefaction

Soil (age)

Late Holocene

Holocen

Pleistocene

Pre-Pleistocen

cti/twi

0-4

4-6

6-8

8-10

>10

PGAm

0,05

Distance to stream (m)

0-50

50-100

100-150

150-200

>200

Vs30

D

C

B

AHP

Stacking

Goal

Subgoal

Factors

Categories

Figure 3. Workflow of the adopted approach for the hazard assessment of earthquake-induced phenomena

Figure 4. Thematic layers of the causative factors that contribute to the likelihood of

earthquake-induced landslides. a) Land use, b) slope aspect, c) distance to streams, d) distance

to roads, e) distance to faults, f) slope position, g) Arias Intensity, h) lithology, and i) slope

angle.

Figure 5. Thematic layers of the causative factors that contribute to the likelihood of soil

liquefaction. a) Age of liquefable soils, b) compound topographic index, c) magnitude

weighted PGA, d) distance to streams, and e) site class.

Figure 6. Earthquake-induced landslide hazard zonation map. a) Mean, b) minimum and c)

maximum estimates.

Figure 7. Liquefaction hazard zonation map. a) Minimum, b) Mean and c) Maximum

estimates.

Figure 8. Hazard zonation map for earthquake-induced phenomena. a) Minimum, b) Mean

and c) Maximum estimates.