The Rimini earthquake of 17th May 1916 (Italy):

from historical data to seismic parameters.

Marco Caciagli – Josep Batlló

Istituto Nazionale di

Geofisica e Vulcanologia

(Italy)

European Seismological Commission ESC 2008, 31st General Assembly - Crete

1916 – Northern Adriatic Earthquakes Sequence

17 May – h: 12:50

Io = VIII ; Me = 5.8

16 August – h: 07:06:14

Io = VIII ; Me=5.7

from May to December 1916

Main events included in the Euroseismos list (A priority)

Tectonic Setting

(from Scrocca et al., 2007 modified)

Seismogenic Source Hypothesis

17 May 1916

Length (km) 8 ; Width (km) 5

Min Depth (km) 3 ; Max Depth (km) 5.5

Strike (deg) 132

Dip (deg) 30

Rake (deg) 90

16 August 1916

Length (km) 8 ; Width (km) 5

Min Depth (km) 3 ; Max Depth (km) 5.5

Strike (deg) 132

Dip (deg) 30

Rake (deg) 90

1916 – Northern Adriatic Earthquakes Sequence

(from Ferrari, 1986)

The Rimini earthquake of 17th May 1916

Me = 5.8 ; Io(MCS) = VIII

Felt Localities 132

Felt Area 90.000 Km2

Damage Zone 3.700 Km2

The Rimini earthquake of 17th May 1916

Epicentral location…previous works

Epicentral Location

1916 BAAS (British Association for Advancement of Sciences)

bulletin was strongly incomplete because of 1st World War

Reconstruction of the bulletin throughout each single Seismic

Station bulletin available

Bulletins collected Station Code Station Location

1) ABA Alger-Bouzareah (Algeria)

2) BID Bidston (England-UK)

3) BRE Breslau - Wroclaw (Poland)

4) BUD Budapest (Hungary)

5) COI Coimbra (Pourtugal)

6) CRT Cartuja - Granada (Spain)

7) DBN De Bildt (Holland)

8) EBR Ebro (Spain)

9) ESK Eskdalemuir (Scotland - UK)

10) FBR Fabra (Spain)

11) GRA Graz - Steiermark (Austria)

12) KEW Kew (England-UK)

13) MAR Marseilles (France)

14) MCI Monte Cassino (Italy)

15) MNC Moncalieri (Italy)

16) PAR Paris - Parc Saint Maur (France)

17) PMP Pompei (Italy)

18) RDP Rocca di Papa (Italy)

19) SFS San Fernando (Spain)

20) STR Strasbourg (France)

21) TAR Taranto (Italy)

22) TOL Toledo (Spain)

23) TRE Trento (Italy)

24) UCC Uccle (Belgium)

25) UPP Uppsala (Sweden)

26) VIE Vienna (Austria)

27) ZAG Zagabria

28) ZUR Zurich (Switzerland)

S waves from bulletinS waves from this work

Location Results

Software used: Hypocenter (Lienert and Havskov, 1995)

44.080 N 13.640 E rms 5.1

Magnitudes

Seismic Moment (Mo) and Moment Magnitude (Mw)Mo(k) = (4πρv3 Ωo) / (G(r) RC) (Keilis-Borok, 1960)

ρ = density ; v = wave velocity ; Ωo = low frequency level ; G (r) = Geometrical spreading ; R

= radiation pattern correction ; C = free surface correction ;

Mw = 2/3 log Mo - 6(Hanks and Kanamori, 1979)

Ms = log (A/T) + 1.66 log Δ° + 3.3(Vanek et al., 1962)

Surface-wave Magnitude

Ms = log (A/G) + 1.656 log Δ° + 1.818 + s(Abe, 1988)

A = maximum trace amplitude (μm) ; T = period (sec) ; G = magnification of the Milne instruments

Δ° = epicentral distance (degrees) ; s = station correction

from Milne instrument

• Selection of the available seismograms from Euroseismos website

• Download of seismograms from SISMOS Website,

• Collection of instrumental constant from station bulletins, station book and seismograms available from Euroseismos website, Euroseismos partners and

other sources

• Digital Vectorization of selected seismograms

• Correction of pen curvature and arm inclination (skew), conversion of traces length (mm) into time (sec)

• Analysis of the waveforms to identify the P and S phases

• Spectral analysis in order to obtain the low-frequency level (Ω0)

• Estimation of the seismic moment (M0) and moment magnitude (Mw)

Stages of work for the Mw estimation

List of seismograms usedStz Lat Stz Long Stz Δ° Δ (km) Instr. Comp To Vo h (damp) drum speed

(mm/min)

1) ALM 36,8525 -2,4598 14,1031 1569,8 Bosch-Omori 25 N 16,86 14,5 0 14,63

2) ALM 36,8525 -2,4598 14,1031 1569,8 Bosch-Omori 25 E 16,72 13,8 0 14,63

3) DBN 52,1017 5,1767 9,6668 1076,0 Galitzin N 25 310 0,5 29

4) DBN 52,1017 5,1767 9,6668 1076,0 Galitzin E 25 310 0,5 28,97

5) EBR 40,8206 0,4933 10,1223 1126,7 Vertical Pendel N 2,6 125 0,4 12

6) EBR 40,8206 0,4933 10,1223 1126,7 Mainka E 7,8 110 0,22 11,9

7) GTT 51,5464 9,9642 7,7541 863,1 Wiechert 17000 N 1,29 1812 0,43 61,38

8) GTT 51,5464 9,9642 7,7541 863,1 Wiechert 1200 E 10,6 160 0,24 10,03

9) GTT 51,5464 9,9642 7,7541 863,1 Wiechert Z 3,6 233 0,24 11,32

10) LEI 51,335 12,3917 7,2169 803,3 Wiechert 1000 N 8 220 0,37 19,15

11) LEI 51,335 12,3917 7,2169 803,3 Wiechert 1000 E 8,5 241 0,27 19,23

12) POT 52,3793 13,0658 8,2311 916,2 Wiechert 1000 N 10 280 0,4 10,72

13) POT 52,3793 13,0658 8,2311 916,2 Wiechert 1000 E 6 330 0,28 9,82

14) STR 48,5836 7,7663 5,9205 659,0 Wiechert 1000 N 8 200 0,5 15

15) STR 48,5836 7,7663 5,9205 659,0 Wiechert 1000 E 8 200 0,5 15

16) STR 48,5836 7,7663 5,9205 659,0 Wiechert 1000 Z 5 200 0,5 15

17) TOL 39,861 -4,017 13,6611 1520,6 Wiechert 1000 NE 10 200 0,46 15,03

18) TOL 39,861 -4,017 13,6611 1520,6 Wiechert 1000 NW 10 200 0,46 15,1

19) UCC 50,7983 4,3594 9,0487 1007,2 Wiechert 1000 N 11,4 156 0,5 14,95

20) UCC 50,7983 4,3594 9,0487 1007,2 Wiechert 1000 E 11,4 165 0,5 14,93

21) UCC 50,7983 4,3594 9,0487 1007,2 Wiechert 1300 Z 4,8 164 0,33 10

22) UPP 59,8583 17,6267 15,9197 1772,0 Wiechert 1000 N 9,1 188 0,36 12,35

23) UPP 59,8583 17,6267 15,9197 1772,0 Wiechert 1000 E 9,1 187 0,38 12,435

24) ZAG 45,8167 15,9830 2,4625 274,1 Wiechert 80 NE 10,1 217 0,48 29,34

25) ZAG 45,8167 15,9830 2,4625 274,1 Wiechert 80 NW 9,8 217 0,5 29,64

Seismograms available by the Euroseismos project

40 seismograms

19 observatories

Seismograms elaboration

After pen curvature and skew correction

The obtained ground displacement spectra were modelled using Brune’s model (Brune, 1970, 1971) by fitting:

U(ω) = Ωo / (1 + (ω / ωc)γ )

Spectra analysis

Ωo = 6,04E-05fc = 0,0204674

Hz

m x

s

Station Component Ω0 Mo Mw

GTT N 2,32E-04 1,01E+18 6,0

GTT E 4,69E-05 8,16E+17

GTT Z 7,18E-05 1,25E+18

POT N 1,55E-05 2,51E+17 5,9

POT E 4,56E-05 6,42E+17

UCC N 6,05E-05 8,51E+17 6,0

UCC E 5,80E-06 8,15E+16

UCC Z 1,35E-04 1,90E+18

STR N 6,95E-05 9,21E+17 6,2

STR E 1,15E-04 1,53E+18

STR Z 2,23E-05 2,96E+17

ZAG NE 9,86E-06 9,18E+17 6,0

ZAG NW 5,18E-06 4,82E+17

TOL NE 1,03E-05 2,21E+17 5,9

TOL NW 3,15E-05 6,77E+17

LEI N 2,43E-05 4,28E+17 5,8

LEI E 1,40E-05 2,47E+17

UPP N 6,19E-05 1,48E+18 6,2

UPP E 6,04E-05 1,44E+18

DBN N 5,25E-05 6,98E+17 6,0

DBN E 4,86E-05 6,45E+17

EBR N 5,65E-04 1,36E+18 6,2

EBR E 3,72E-05 4,85E+17

ALM N 2,34E-05 5,66E+17 6,0

ALM E 2,34E-05 5,23E+17

Seismograms analysis results

Mo = 1,14E+18 (Nm)

Mw = 6.0 ± 0.1

Stz (milne) component Ms

KEW E 5,82

SFS E 5,68

*BID E 5,97

TOL E 5,87

Station Comp. Ms (comp) Ms

CRT N 5,96 5,96

PAR N 5,91 5,88

PAR E 5,86

ABA E 5,16 5,11

ABA N 5,08

MAR E 5,81 5,89

MAR N 5,97

GRA E 0,23 5,35

GRA N 5,47

COI E 6,10 6,14

COI N 6,19

TOL NW 5,63 5,58

TOL NE 5,53

FBR E 5,88 5,89

FBR N 5,91

STR E 6,69 6,59

STR N 6,51

DBN E 6,05 6,13

DBN N 6,24

UCC E 5,80 5,8

UCC Z 5,80

UPP E 5,84 5,84

VIE E 5,92 6,00

VIE N 6,08

Ms calculated from Milne instruments

Surface-wave Magnitude

Ms(Milne) = 5.8 ± 0.1

Ms = 5.8 ± 0.3

List of Ms calculated from each station

Conclusions and outlooks

• The epicentral location of the 17 May 1916 Rimini earthquake is clearly in the sea. The instrumental location error is quite large but the solution is robust.

• The comparison of the bulletins data with the original seismograms collected allowed us to reduce the misfits: projects like Euroseismos-type must be encouraged.

• For the first time Mw and Ms magnitudes has been instrumentally calculated. These results increase the databank of large earthquakes with calculated Mw.

Future work

We should invert the waveform for moment tensor determination and such procedure should be applied to other earthquakes of the “Northern Adriatic Sequence”.