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Seismicity of Eastern Alps and North western Dinaric Alps

Deniz Ertuncay, Blaž Vicic and Giovanni Costa

University of Trieste, Department of Mathematics and Geoscience, Trieste, Italy

Our study region is placed on Adriatic Plate and the boundaries are Dinaric Orogenic Belt, Carnic, Tolmezzo and

Julian Alps. The area has normal, reverse and strike slip faults which can generate big earthquakes such as 1976

Mw 6.5 Friuli Earthquake, 1998 and 2004 Bovec-Krn Earthquakes. The area is located between Austria, Slovenia

and Italy. Our group, SEISRAM, has dense seismic station on the Italian part of the region and has access to get data

from other countries on the region. We are monitoring the region with a good coverage by collaborating with other

institutes on the Ce3RN project which we are also part of. We can detect lower than 0.5 Magnitude earthquakes.

We use our database and other seismological centers to investigate the seismicity of the region between 1960

and 2016. Gutenberg – Richter magnitude frequency relationship is applied in order to get a knowledge about the

seismicity of Friuli region. By using the database ‘a’ and ‘b’ values of the region are found. Same procedure is done

for each fault line, separately. Magnitude of completeness for each fault are calculated. Calculation of earthquake

probabilities for fixed periodic times for possible from magnitude 3 to magnitude 6 earthquakes. All calculations

are done by using Matlab based ZMAP program.

 

Evidence of a tectonic transient within the Idrija fault system in Western Slovenia

Blaž Vicic (1), Giovanni Costa (1) and Abdelkrim Aoudia (2)

(1) University of Trieste, Department of Matematics and Geosciences, Trieste, Italy, (2) International Centre for Theoretical Physics, Earth System Physics Section, Trieste, Italy

Western Slovenia and North-eastern Italy are areas of medium rate seismicity with rare historic earthquakes of

higher magnitudes. From mainly reverse component faulting in north-western part of the region where 1976 Friuli

earthquakes took place, tectonic regime changes to mostly strike-slip faulting in the Dinaric region, continuing

towards southeast. In the northern part of the Idrija fault system, which represent the broader Dinaric strike-slip

system there were two strong earthquakes in the recent times - Mw=5.6 1998 and Mw=5.2 2004 earthquakes.

Further to the south, along the Idrija fault system, Idrija fault is the causative fault of 1511 Mw=6.8 earthquake.

The southeastern most part of the Idrija fault system produced a Mw=5.2 earthquake in 1926 and few historic

Mw>4 earthquakes.

Since 2004 Mw=5.2 earthquake, no stronger earthquakes were recorded in the region covered by dense

seismic network. Seismicity is mostly concentrated in Friuli region and north-western part of Idrija fault system -

mostly on the Ravne fault which is the causative fault for the 1998 and 2004 earthquakes. In the central part of the

fault system no strong or moderate earthquakes were recorded, except of an earthquake along the Idrija fault in

2014 of magnitude 3.4. Low magnitude background seismicity is burst like with no apparent temporal or spatial

distribution. Seismicity of the southern part of Idrija fault system is again a bit higher than in the central part of

the fault system with earthquakes up to Mw=4.4 that happened in 2014.

In this study, detailed analysis of the seismicity is performed with manual relocation of the seismicity in

the period between 2006 and 2016. With manual inspection of the waveform data, slight temporal clustering

of seismicity is observed. We use a template algorithm method to increase the detection rate of the seismicity.

Templates of seismicity in the north-western and south-eastern part of Idrija fault system are created. The

continuous waveform data within the period 2006-2016 is investigated. As a result, high temporal correlation

in the years 2009 and 2010 of different bursts of seismicity all along Idrija fault system is observed. These

bursts of semsicity located at seismogenic depths do also correlate well with clear changes within the pattern of

surface deformation as exhibited by the continuous recording on the tm-71 extensometer in Postojna cave. Four

small clusters of seismicity start in late 2009 in north-western part of Idrija fault system, migrating along the

neighbouring faults in the region through 2010, together forming a swarm-like cluster of seismicity. In the same

time period seismic swarm took place along Predjama fault, which is monitored by the Postojna extensometer

and lasts more than 1 year. Finally, in September 2010 elevated seismicity of Idrija fault system finishes with two

Mw>3.5 earthquakes in the south-eastern part of Idrija fault system.

In this study we report a clear time dependent tectonic transient that took place along the Idrija fault sys-
tem between 2009 and 2010 and discuss the physics of earthquake swarms vs. the mechanics of active faults and

the related seismogenesis.

 

Estimation of regression laws for ground motion parameters using as case of study the Amatrice earthquake

Lara Tiberi and Giovanni Costa

University of Trieste, Dipartimento di Matematica e Geoscienze, Trieste, Italy (lara.tiberi@gmail.com)

The possibility to directly associate the damages to the ground motion parameters is always a great challenge, in

particular for civil protections. Indeed a ground motion parameter, estimated in near real time that can express the

damages occurred after an earthquake, is fundamental to arrange the first assistance after an event. The aim of this

work is to contribute to the estimation of the ground motion parameter that better describes the observed intensity,

immediately after an event. This can be done calculating for each ground motion parameter estimated in a near

real time mode a regression law which correlates the above-mentioned parameter to the observed macro-seismic

intensity. This estimation is done collecting high quality accelerometric data in near field, filtering them at different

frequency steps. The regression laws are calculated using two different techniques: the non linear least-squares

(NLLS) Marquardt-Levenberg algorithm and the orthogonal distance methodology (ODR). The limits of the first

methodology are the needed of initial values for the parameters a and b (set 1.0 in this study), and the constraint

that the independent variable must be known with greater accuracy than the dependent variable. While the second

algorithm is based on the estimation of the errors perpendicular to the line, rather than just vertically. The vertical

errors are just the errors in the ‘y’ direction, so only for the dependent variable whereas the perpendicular errors

take into account errors for both the variables, the dependent and the independent. This makes possible also to

directly invert the relation, so the a and b values can be used also to express the gmps as function of I. For each

law the standard deviation and R2 value are estimated in order to test the quality and the reliability of the found

relation. The Amatrice earthquake of 24th August of 2016 is used as case of study to test the goodness of the

calculated regression laws.