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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Earthquake rates in ItalyEarthquake rates in Italyas derived from different approachesas derived from different approaches
Gianluca Valensise and Michele M. C. CarafaGianluca Valensise and Michele M. C. CarafaIstituto Nazionale di Geofisica e Vulcanologia, RomaIstituto Nazionale di Geofisica e Vulcanologia, Roma
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
• Assessing earthquake rates is made Assessing earthquake rates is made difficult by the incompleteness of all difficult by the incompleteness of all datasets that can be used in the datasets that can be used in the calculation.calculation.
• This is especially true in Italy, due to the This is especially true in Italy, due to the limited tectonic strains, to the complexity limited tectonic strains, to the complexity of the tectonic regime and to the existence of the tectonic regime and to the existence of significant tectonic deformation offshore.of significant tectonic deformation offshore.
• We aim at demonstrating that a carefully We aim at demonstrating that a carefully collected set of moment rate data at collected set of moment rate data at national scale may be used to reduce the national scale may be used to reduce the uncertainties associated with each uncertainties associated with each individual dataset.individual dataset.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
A little history…A little history…
From Corriere della SeraFrom Corriere della Sera24 September 199924 September 1999
Following the 1997 Following the 1997 Colfiorito earthquakes, DPC Colfiorito earthquakes, DPC
officials asked the officials asked the seismological community to seismological community to identify priority areas for a identify priority areas for a
state-driven financial state-driven financial intervention aimed at intervention aimed at reinforcing public and reinforcing public and
private buildings. private buildings.
INGV scientists responded INGV scientists responded with their early results on with their early results on
seismicity patterns, seismicity patterns, distribution of active faults, distribution of active faults,
fault segmentation in fault segmentation in relation with historical relation with historical
earthquakes, and on the earthquakes, and on the stress field.stress field.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
This request was This request was prompted by the prompted by the
publication of the publication of the returns of a returns of a
vulnerability census of vulnerability census of “public, strategic and “public, strategic and
special buildings” over special buildings” over the most seismic-prone the most seismic-prone
areas of central and areas of central and southern Italy. southern Italy.
The census highlighted The census highlighted significant vulnerability significant vulnerability
differences in among differences in among different portions of the different portions of the
country. country.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Earthquake probabilitiesEarthquake probabilitiesoror
Earthquake rates?Earthquake rates?
An earthquake rate is the number of quakes per unit time An earthquake rate is the number of quakes per unit time (usually one year) within a given M range (e.g. 5.5 to 8.0) (usually one year) within a given M range (e.g. 5.5 to 8.0) in a given area.in a given area.
Earthquake probabilities express the likelihood of an Earthquake probabilities express the likelihood of an earthquake of magnitude equal or larger than a given earthquake of magnitude equal or larger than a given threshold occurring within a specified time interval in a threshold occurring within a specified time interval in a given area.given area.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
In time-independent seismic hazard assessment, the higher the In time-independent seismic hazard assessment, the higher the rate, the higher the probability.rate, the higher the probability.
For a given earthquake rate, however, the probability of an For a given earthquake rate, however, the probability of an earthquake of size M is controlled by the earthquake of size M is controlled by the bb of the Gutenberg- of the Gutenberg-Richter relation calculated for the region of interest: a smaller Richter relation calculated for the region of interest: a smaller bb will result in larger, more infrequent (and hence less likely) will result in larger, more infrequent (and hence less likely) earthquakes, and viceversa.earthquakes, and viceversa.
In time-dependent seismic hazard, for the same given earthquake In time-dependent seismic hazard, for the same given earthquake rate the actual probability associated with an earthquake of rate the actual probability associated with an earthquake of magnitude M will also be a function of the previous seismic history magnitude M will also be a function of the previous seismic history (e.g. elapsed time).(e.g. elapsed time).
This presentation deals with This presentation deals with earthquake rates, not probabilities earthquake rates, not probabilities
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
DPC-INGV Agreement 2000-2003DPC-INGV Agreement 2000-2003
““Terremoti probabili in Italia tra l'anno 2000 e il 2030: Terremoti probabili in Italia tra l'anno 2000 e il 2030: elementi per la definizione di prioritelementi per la definizione di prioritàà degli interventi di degli interventi di
riduzione del rischio sismicoriduzione del rischio sismico””
““Probable earthquakes in Italy between the year 2000 and Probable earthquakes in Italy between the year 2000 and 2030: elements for the definition of priorities of intervention 2030: elements for the definition of priorities of intervention
for seismic risk mitigationfor seismic risk mitigation””
(coordinated by Alessandro Amato, INGV, and Giulio Selvaggi, INGV)(coordinated by Alessandro Amato, INGV, and Giulio Selvaggi, INGV)
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
DPC-INGV Agreement 2004-2006DPC-INGV Agreement 2004-2006
““Valutazione del potenziale sismogenetico e probabilitValutazione del potenziale sismogenetico e probabilitàà dei dei forti terremoti in Italia”forti terremoti in Italia”
““EvEvaluation of the seismogenic potential and probability of aluation of the seismogenic potential and probability of a large earthquake in Italya large earthquake in Italy””
(coordinated by Dario Slejko, INOGS, and Gianluca Valensise, INGV)(coordinated by Dario Slejko, INOGS, and Gianluca Valensise, INGV)
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
DPC-INGV Agreement 2007-2009DPC-INGV Agreement 2007-2009
““Determinazione del potenziale sismogenetico in Italia per il Determinazione del potenziale sismogenetico in Italia per il calcolo della pericolositcalcolo della pericolositàà sismica” sismica”
““Determination of the seismogenic potential in Italy for the Determination of the seismogenic potential in Italy for the calculation of seismic hazardcalculation of seismic hazard””
(coordinated by Salvatore Barba, INGV, and Carlo Doglioni, UniRM1)(coordinated by Salvatore Barba, INGV, and Carlo Doglioni, UniRM1)
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
• GPS velocities, strain and slip rates (RING & other networks)GPS velocities, strain and slip rates (RING & other networks)
• Composite Seismogenic Sources & their slip rates (DISS)Composite Seismogenic Sources & their slip rates (DISS)
• Results of Finite Element geodynamic ModelingResults of Finite Element geodynamic Modeling
• Updated earthquake cataloguesUpdated earthquake catalogues
Some Research Units of project S1 supplied independent Some Research Units of project S1 supplied independent datasets at national scale that could be used to obtain datasets at national scale that could be used to obtain countrywide moment rate maps, includingcountrywide moment rate maps, including
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
GPS velocities - IGPS velocities - I
RU 1.03RU 1.03
Nicola D’AgostinoNicola D’Agostino
INGVINGV
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
GPS velocities - IIGPS velocities - II
RU 1.04RU 1.04
Roberto DevotiRoberto Devoti
INGVINGV
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
GPS velocities - IIIGPS velocities - III
RU T.01RU T.01
Steven WardSteven Ward
UC Santa CruzUC Santa Cruz
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Strain ratesStrain rates
RU 1.02RU 1.02
Alessandro CaporaliAlessandro Caporali
Univ. of PadovaUniv. of Padova
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Slip ratesSlip rates
RU 1.03RU 1.03
Nicola D’AgostinoNicola D’Agostino
Enrico SerpelloniEnrico Serpelloni
INGVINGV
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Composite Seismogenic Sources (DISS)Composite Seismogenic Sources (DISS)
RU 3.01RU 3.01
Roberto BasiliRoberto Basili
RU 3.12RU 3.12
Paola VannoliPaola Vannoli
INGVINGV
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Geodynamic modelingGeodynamic modeling
RU 5.03RU 5.03
Antonella MegnaAntonella Megna
INGVINGV
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Updated eq catalogue (CPTI04 vs CPTI10)Updated eq catalogue (CPTI04 vs CPTI10)
RU S.01RU S.01
Paolo GasperiniPaolo Gasperini
Univ. of BolognaUniv. of Bologna
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
ElaborationsElaborations
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Kostrov’s moment methodKostrov’s moment methodSummation of moment rates obtained from strain rates derived Summation of moment rates obtained from strain rates derived
from GPS and Finite Element geodynamic Modeling (FEM) using from GPS and Finite Element geodynamic Modeling (FEM) using
Kostrov’s formula (1974).Kostrov’s formula (1974).
Slip-based moment methodSlip-based moment methodSummation of slip over fault surfaces from DISS CompositeSummation of slip over fault surfaces from DISS Composite
Seismogenic Sources, block modeling and faults from FEM.Seismogenic Sources, block modeling and faults from FEM.
Seismic moment methodSeismic moment methodSummation of seismic moment for 400 years of historicalSummation of seismic moment for 400 years of historical
earthquakes based on Hanks and Kanamori’s (1979) formula.earthquakes based on Hanks and Kanamori’s (1979) formula.
Data of different categories can be used to derive a moment Data of different categories can be used to derive a moment rate map based on one of the following three methods:rate map based on one of the following three methods:
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
For any area of Italy we can determine an For any area of Italy we can determine an Average Moment RateAverage Moment Rate with with all moment rates obtained from indipendent datasets (GPS strains, slip all moment rates obtained from indipendent datasets (GPS strains, slip data, geodynamic modeling, block modeling), and a data, geodynamic modeling, block modeling), and a Seismic Moment Seismic Moment RateRate based on a 400 years catalogue window. We consider these as based on a 400 years catalogue window. We consider these as two end-memberstwo end-members for all subsequent analyses. for all subsequent analyses.
The Average Moment Rate can be used to calculate the earthquake The Average Moment Rate can be used to calculate the earthquake rate only after assessing how much energy actually goes into rate only after assessing how much energy actually goes into earthquake production, i.e. the coupling factor earthquake production, i.e. the coupling factor cc::
c = Seismic Moment Rate (SMR)/Average Moment Rate (AMR)c = Seismic Moment Rate (SMR)/Average Moment Rate (AMR)
The seismic couplingThe seismic coupling c c is often assumed to be constant over large is often assumed to be constant over large regions (e.g. Italy). This parameter, however, exhibits a large regions (e.g. Italy). This parameter, however, exhibits a large variability worldwide and appears largely controlled by the prevalent variability worldwide and appears largely controlled by the prevalent faulting mechanism. Neglecting this variability may results in severe faulting mechanism. Neglecting this variability may results in severe over- or under-estimation of the earthquake rates.over- or under-estimation of the earthquake rates.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Defining seismic coupling within ZS9 zonesDefining seismic coupling within ZS9 zones
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Seismic coupling is obtained by:Seismic coupling is obtained by:
• summing up the summing up the Seismic Moment RateSeismic Moment Rate (SMR) of all ZSs (SMR) of all ZSs sharing the same prevalent focal mechanism; sharing the same prevalent focal mechanism;
• summing up the summing up the Average Moment RateAverage Moment Rate (AMR) of all ZSs (AMR) of all ZSs sharing the same prevalent focal mechanism (same as sharing the same prevalent focal mechanism (same as above); above);
• calculating calculating cc as the ratio of SMR and AMR; as the ratio of SMR and AMR;
• for areas with undetermined mechanism, the calculation is for areas with undetermined mechanism, the calculation is done using all SMRs and AMRs.done using all SMRs and AMRs.
In principle this procedure yields 3 “characteristic” coupling In principle this procedure yields 3 “characteristic” coupling factors factors cc associated with reverse, strike-slip, and normal associated with reverse, strike-slip, and normal faulting, plus an estimate for areas of undetermined faulting, plus an estimate for areas of undetermined mechanisms.mechanisms.
Defining seismic coupling within ZS9 zonesDefining seismic coupling within ZS9 zones
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Average Kostrov-slip methodAverage Kostrov-slip method(AMR)(AMR)
(N m)/yr
Seismic moment methodSeismic moment method(SMR)(SMR)vs
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Seismic coupling Seismic coupling cc (M (MSMRSMR/M/MAMRAMR))averaged on areas having the same deformation styleaveraged on areas having the same deformation style
0.25 for reverse faulting0.25 for reverse faulting0.90 for strike-slip0.90 for strike-slip0.98 for normal faulting0.98 for normal faulting
(0.80 for undetermined faulting)(0.80 for undetermined faulting)
> 0.8 0.4 - 0.8 0.0 - 0.4
Coupling factor c
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
To calculate earthquakes rates from both AMR (via the To calculate earthquakes rates from both AMR (via the seismic coupling seismic coupling cc) and SMR (directly) we used the ) and SMR (directly) we used the formula proposed by Ward (1994):formula proposed by Ward (1994):
Number of eqs of magnitude > M
b of Gutenberg-Richter relation
Moment rate
Max expected M for the given region
Calculating earthquake ratesCalculating earthquake rates
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Case historiesCase histories
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
• Incomplete earthquake catalogue? Incomplete earthquake catalogue?
• Average Moment Rate overestimated due to scattered data?Average Moment Rate overestimated due to scattered data?
• Inappropriate assignment of prevalent faulting style/seismic coupling?Inappropriate assignment of prevalent faulting style/seismic coupling?
?
The case of the ZS911 “Tortona-Bobbio”The case of the ZS911 “Tortona-Bobbio”
Catalogue
AMR x c for varying Mmax
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
The case of the Messina StraitsThe case of the Messina Straits
Avg.
Histo
rical
eq
s
DIS
S
FEM
GPS
Mom
ent
rate
(1
01
6 N
m/y
r)
Good agreement between Average and Seismic Moment RateGood agreement between Average and Seismic Moment Rate
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Catalogue
AMR x c for Mmax 7.2-7.3
The case of the Messina StraitsThe case of the Messina Straits
Earthquake rate is stable regardless of whether it is obtained from Earthquake rate is stable regardless of whether it is obtained from seismicity or from all the other available dataseismicity or from all the other available data
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
• The uncertanties associated with earthquake The uncertanties associated with earthquake catalogues (completeness, location and size of catalogues (completeness, location and size of individual events), andindividual events), and
• the need for merging and smoothing widely different the need for merging and smoothing widely different categories of data (GPS, active faults, geodynamic categories of data (GPS, active faults, geodynamic models)models)
suggestedsuggested
to proceed calculating earthquake rates using larger to proceed calculating earthquake rates using larger zones than the ZSs.zones than the ZSs.
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Homogeneous geological macroregionsHomogeneous geological macroregions
1122
33
44
5566
7788
FromFrom Basili Basili [2007] [2007]
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Mean absolute deviationMean absolute deviationAverage Moment RateAverage Moment Rate
Average Moment RateAverage Moment Ratefor geological macroregionsfor geological macroregions
We have a problem in the Calabrian Arc!!!!We have a problem in the Calabrian Arc!!!!
0-25
25-50
50-75
>75
(1016 N m)/yr
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Moment rate in the Calabrian ArcMoment rate in the Calabrian ArcReasons for a large scatterReasons for a large scatter
Histo
rical e
qs
DIS
S
FEM
Blo
ck mod
elin
g
GPS
Significant thrust activity in the Ionian Sea imaged onlySignificant thrust activity in the Ionian Sea imaged onlyby geologic data/geodynamic modelsby geologic data/geodynamic models
Mom
ent
rate
(1
01
6 N
m/y
r)
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Seismic Moment RateSeismic Moment Ratevsvs
Average Moment RateAverage Moment Rate
Seismic coupling is nearly total only in extensional domains (6) Seismic coupling is nearly total only in extensional domains (6) and very low or close to zero in compressional domains (1, 2, 3)and very low or close to zero in compressional domains (1, 2, 3)
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INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
The case of the Ionian ArcThe case of the Ionian Arc
The extensive active thrusting in the Ionian Arc suggests that the The extensive active thrusting in the Ionian Arc suggests that the seismic coupling of this area is lower than the seismic coupling of this area is lower than the cc calculated for calculated for macroregion #7, in agreement with the very low seismicity.macroregion #7, in agreement with the very low seismicity.
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ulca
nolo
gia
INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
Data supplied by S1 RUs allow earthquake rates to be Data supplied by S1 RUs allow earthquake rates to be calculated with reasonable approximation and measurable calculated with reasonable approximation and measurable uncertainties everywhere in Italy.uncertainties everywhere in Italy.
We deliberately highlighted We deliberately highlighted “problematic“problematic cases” (ZS911 or cases” (ZS911 or Ionian Arc) suggesting:Ionian Arc) suggesting:
• that each mismatching case must be considered that each mismatching case must be considered individually to understand the reasons for it (e.g. individually to understand the reasons for it (e.g. unreliable GPS data, unidentified active faults, incomplete unreliable GPS data, unidentified active faults, incomplete earthquake catalogue, etc.);earthquake catalogue, etc.);
• that seismic coupling is a crucial parameter that must be that seismic coupling is a crucial parameter that must be assessed for the smallest/most homogeneous possible assessed for the smallest/most homogeneous possible region;region;
• that very active and quickly deforming offshore areas such that very active and quickly deforming offshore areas such as the Ionian Arc (but also the southern Tyrrhenian) need as the Ionian Arc (but also the southern Tyrrhenian) need to be considered very carefully for seismic hazard to be considered very carefully for seismic hazard assessment.assessment.
Istituto
Nazio
nale
di G
eofisica
e V
ulca
nolo
gia
Istituto
Nazio
nale
di G
eofisica
e V
ulca
nolo
gia
INGV-DPC 2007‐2009 Agreement - Final Meeting of the Seismological Projects - Rome, 30 June-2 July 2010
• Calculating earthquake rates is a fundamental task in Calculating earthquake rates is a fundamental task in modern Applied Seismology. The results of S1 demonstrate modern Applied Seismology. The results of S1 demonstrate that doing it properly requires good quality, that doing it properly requires good quality, homogeneously collected data of widely different nature.homogeneously collected data of widely different nature.
ConclusionsConclusions
• Not only the data have to be good, they also need to be Not only the data have to be good, they also need to be organized in well accessible georeferenced databases. organized in well accessible georeferenced databases. Natural uncertainties are already too big to have to deal Natural uncertainties are already too big to have to deal also with the scatter arising from different ways of also with the scatter arising from different ways of elaborating or plotting the data.elaborating or plotting the data.
• We believe S1 will have an important structuring effect on We believe S1 will have an important structuring effect on research in Applied Seismology in Italy, marking a research in Applied Seismology in Italy, marking a significant progress over the previous two “parent significant progress over the previous two “parent projects” (2000-2003 and 2004-2006 INGV-DPC projects” (2000-2003 and 2004-2006 INGV-DPC Agreements). S1 also highligted the importance of striking Agreements). S1 also highligted the importance of striking a balance between basic investigations and the a balance between basic investigations and the elaborations leading to results that may be of immediate elaborations leading to results that may be of immediate interest for DPC.interest for DPC.
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