Istituto Nazionale di Geofisica e Vulcanologia INGV-DPC 20072009 Agreement - Final Meeting of the...

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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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• 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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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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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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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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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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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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““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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““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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• 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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GPS velocities - IGPS velocities - I

RU 1.03RU 1.03

Nicola D’AgostinoNicola D’Agostino

INGVINGV

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GPS velocities - IIGPS velocities - II

RU 1.04RU 1.04

Roberto DevotiRoberto Devoti

INGVINGV

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GPS velocities - IIIGPS velocities - III

RU T.01RU T.01

Steven WardSteven Ward

UC Santa CruzUC Santa Cruz

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Strain ratesStrain rates

RU 1.02RU 1.02

Alessandro CaporaliAlessandro Caporali

Univ. of PadovaUniv. of Padova

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Slip ratesSlip rates

RU 1.03RU 1.03

Nicola D’AgostinoNicola D’Agostino

Enrico SerpelloniEnrico Serpelloni

INGVINGV

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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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Geodynamic modelingGeodynamic modeling

RU 5.03RU 5.03

Antonella MegnaAntonella Megna

INGVINGV

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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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ElaborationsElaborations

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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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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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Defining seismic coupling within ZS9 zonesDefining seismic coupling within ZS9 zones

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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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Average Kostrov-slip methodAverage Kostrov-slip method(AMR)(AMR)

(N m)/yr

Seismic moment methodSeismic moment method(SMR)(SMR)vs

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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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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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Case historiesCase histories

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• 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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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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• 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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Homogeneous geological macroregionsHomogeneous geological macroregions

1122

33

44

5566

7788

FromFrom Basili Basili [2007] [2007]

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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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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

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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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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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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.

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• 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.

Istituto Nazionale di Geofisica e Vulcanologia INGV-DPC 20072009 Agreement - Final Meeting of the...

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