Present-day stress in the area of L’Aquila April 6 2009 ...42°N 07Km N 2009 L’Aquila sequence...
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MORE INFO IN: MARIUCCI M.T., MONTONE P., PIERDOMINICI S. (2010)- Present-day stress in the surroundings of 2009 L’Aquila seismic sequence (Italy). Geophysical Journal Internaonal, on-line July 2010, doi: 10.1111/j.1365-246X.2010.04679.x. Boncio P. et al. (2004). Ann. Geophys., 47, 1723–1742 Centamore E. et al. (1991). Studi Geologici Camer, Spec. Vol. CROP 11, 1991/2, 125–131 Chiarabba C. et al. (2009). Geophys. Res. Le., 36, L18308, doi:101029/2009GL039627 CPTI Working Group (2004), hp://emidius.mi.ingv.it/CPTI Emergeo Working Group (2010). Terra Nova, 22, 43–51, doi: 10.1111/j.1365-3121.2009.00915.x hp://www.eas.slu.edu/Earthquake Center/MECH.IT/ ISIDe, hp://iside.rm.ingv.it/iside/standard/index.jsp Montone P. et al. (2004). J. Geophys. Res., 109(B10410), doi: 10.1029/2003JB002703 Pizzi A. & Galadini F. (2009). Tectonophysics, 476(1–2), 304–319, doi:10.1016/j.tecto.2009.03.018 Pondrelli S. et al. (2010). Geophys. J. Int., 180, 238–242, doi:10.1111/j.1365-246X.2009.04418.x Many thanks are due to ENI S.p.A. to provide the borehole data. This work was carried out in the frame of the MIUR-FIRB Project ‘Research and Development of New Technologies for Projecon and Defense of Territory fromNatural Risks’ (WP-C3, coordinator Paola Montone). Acknowledgments References Valnerina thrust Olevano-Antrodoco Sibillini thrust Sangro- Volturno thrust Laga Fault Mt. Bove Gran Sasso thrust Paganica Fault Colfiorito Norcia L’Aquila Maiella Sulmona Basin Chieti Adriatic Sea Fucino Basin Main normal fault (Quaternary/active) Main transpressive/thrust front (Neogene) Shmin from earthquakes Shmin from borehole breakouts 13°E 43°N 42°N 14°E 0 km 20 N 19970926 09:40 Mw6.0 19970926 00:33 Mw5.7 19971014 Mw5.6 20090409 Mw5.4 19790919 Mw5.8 20090406 Mw6.3 20090407 Mw5.5 19150113 Mw6.9 V1 C1 ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !!! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! !! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! !!! ! ! ! !! ! ! ! ! ! ! ! !! !!! ! !! ! !! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! !!! !!! ! !! !! ! ! !! ! ! ! ! !! ! ! ! !!!! !! ! ! ! !! ! ! ! ! ! ! ! !!! ! ! ! !! ! !!!!! !!! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ Barisciano Castel del Monte Assergi Arischia Coppito Preturo Paganica-Tempera o Poggi Roio Montereale Marana Ovindoli Pizzoli Poggio Picenze Ne' Vestini Isola del Gran Sasso d'Italia Onna Campotosto Lucoli S. Panfilo Bazzano Rocca di Cambio Collebrincioni Villa S. A ngelo Tione degli Abruzzi Sinizzo Lake Campotosto Lake L' uila Mt. Ocre 370000 370000 390000 390000 4680000 4680000 4700000 4700000 Ü Fossa Demetrio S. Pianola Aq i Mont cchio ! ( ! ( ! ( ¯ ¯ ¯ Projection UTM Zone 33 - Datum WGS 1984 tectonic rupture secondary effect no coseismic effect Quaternary normal fault LEGEND 0 4 8 Km A-186 measures, 77 max 107 measures, 56 max B- 32 measures, 12 max D- 7 measures, 2 max C- all data 1 2 7 3 4 6 8 9 10 12 13 14 15 16 17 18 19 20 5 11 Campotosto Lake 0 2.5 Km N Cittareale Montereale Borbona Amatrice Accumoli Quaternary deposits “Laga” Fm., clayey-arenaceous member (lower Messinian) Normal fault Thrust fault Focal mechanism solution “Maiolica” limestone and “Diaspri” (lower Cretaceous-Dogger) “Fucoidi” marls (Albian-Aptian) “Scaglia” marly limestone (Eocene-upper Cretaceous) “Laga” Fm. , arenaceous-clayey member (lower Messinian) “Laga” Fm. , arenaceous member (lower Messinian) “Orbulina” or “Pteropodi” marls (Messinian-Tortonian) “Cerrogna” marls (upper-middle Miocene) Shmin orientation a) V1 C1 Olevano-Antrodoco thrust Mt.Gorzano Campotosto Lake GRAN SASSO L’AQUILA Mw5.4 Mw5.5 Mw6.3 b) Shmin= N081 + 22° L= 962 m Shmin= N074 + 10° L= 43 m “Laga” (lower Messinian) Marl units (Tortonian - Langhian) “Massiccio” (lower Lias) “Dolomites” (middle - lower Triassic) Rose Plot log analysed Breakout interval Breakout orientation “Scaglia” (Oligocene - upper Cretaceous) “Maiolica” and “Diaspri” (lower Cretaceous - middle Lias) 2000 0 m 1000 3000 4000 5000 6000 V 1 C 1 g.l. 1160 m a.s.l. g.l. 1525 m a.s.l. " / 1915 1904 1762 1950 1703 1703 1730 1979 1461 1639 1599 1349 09/04/23 21:49 Mw 4.3 09/04/23 14:14 Mw 4.1 09/04/07 17:47 Mw 5.5 09/04/08 04:27 Mw 4.0 09/04/09 03:15 Mw 4.4 09/04/06 07:17 Mw 4.2 09/04/06 01:32 Mw 6.3 09/03/30 Mw 4.4 09/07/12 08:38 Mw 4.3 09/04/07 09:26 Mw 5.1 09/04/05 20:48 Mw 4.2 09/04/06 16:38 Mw 4.4 09/04/06 03:56 Mw 4.5 09/04/07 21:34 Mw 4.5 09/04/06 02:37 Mw 5.1 09/04/09 04:32 Mw 4.3 09/06/22 20:58 Mw 4.7 09/04/06 23:15 Mw 5.1 09/04/10 03:22 Mw 3.9 09/04/09 00:52 Mw 5.4 09/07/03 11:03 Mw 4.1 09/04/14 20:14 Mw 4.0 09/04/13 21:14 Mw 5.0 09/04/09 19:38 Mw 5.2 09/04/08 22:56 Mw 4.1 09/04/15 22:53 Mw 4.1 " / " / " / " / " / " / " / " / " / " / " / " / L’AQUILA Barete Cittareale Montereale Pizzoli Scoppito Paganica Fossa Tornimparte Barisciano Ovindoli Avezzano GRAN SASSO V1 C1 13.5°E 13°E 42°N 0 7 Km N 2009 L’Aquila sequence Mainshocks Focal mechanism solutions Wells M<3.0 3.0<M<3.5 3.5<M<4.5 4.5<M<5.0 M>5.0 Foreshocks Ml<3.0 3.0<Ml<3.5 Ml>3.5 Historical earthquakes M>5.5 V1 C1 Campo Imperatore Gran Sasso a) A n t r o d o c o Olevano A B C 0 10 Km N 186 coseismic rupture orientations N Depth (km) Mw 0 0 5 10 15 20 20 40 60 80 100 120 140 160 180 Azimuth Azimuth 0 5 10 15 20 25 30 35 0 10 110 120 130 140 150 160 170 180 20 30 40 50 60 70 80 90 100 Number Azimuth b) c) V1 σ3 C1 C 0 20 40 60 80 100 120 140 160 180 0 1 2 3 4 5 6 7 d) B A T-axis 2009 L’Aquila sequence: Shmin-breakout orientation Active Fault Thrust Fault Mw>5.2 3.0<Mw<4.0 2.7<Mw<3.0 CMT solution 4.0<Mw<5.2 σ3 from past sequences 13.5°E 42.4°N L’AQUILA Montereale Amatrice Pizzoli Paganica Fossa Tornimparte Barisciano Raiale str eam Tempera Paganica 13.48° E 13.48° E 13.47° E 13.47° E 42.37° N 0 250 500 125 Meters Fossa Pianola Bazzano Paganica L'Aquila Monticchio Poggio Picenze Poggio di Roio Collebrincioni Aqueduct L’Aquila 2009 seismic sequence (Chiarabba et al., 2009) with focal mechanism soluons of the main events (Pondrelli et al., 2010). Red circles are the three mainshocks; light blue circles are the foreshocks of the sequence (hp://iside.rm.ingv.it/); yellow squares represent the historical seismicity with M ≥ 5.5 (CPTI Working Group 2004); yellow stars are the well locaons. Seismotectonic seng of the area. (a) 170 TDMT T-axis orientaons of the 2009 L’Aquila sequence (hp://www.eas.slu.edu/Earthquake Center/MECH.IT/); CMT focal mechanisms of the three mainshocks (A, B, C; Pondrelli et al., 2010); σ3 orientaon from the 1992, 1994 and 1996 seismic sequences (Boncio et al., 2004); the Shmin orientaon inferred from breakout analysis in the two deep wells Campotosto (C1) and Varoni (V1) and the major acve normal and thrust faults. In the inset: the rose plot shows the orientaon of the 186 coseismic rup- tures idenfied at surface (Emergeo Working Group, 2010). (b) Azimuth frequency histogram of TDMT T-axis orientaons; the red lines represent the T-axis orientaons from CMT data of main events (Pondrelli et al., 2010). (c) TDMT T-axis azimuth distribuon versus depth together with the Shmin orientaon from boreholes breakouts (yellow stars) and the σ3 from the past sequences (red circle). (d) TDMT T-axis versus their magnitude. (a) Geological and structural map of the study area (redrawn aſter Centamore et al., 1991) with Shmin orientaons from breakout analysis. The inset shows the locaon and the focal mechanisms of the three 2009 mainshocks. (b) Stragraphic sketch and breakout analysis of the Varoni 1 (V1) and Campotosto 1 (C1) wells. The two rose plots show breakout orientaons scaled for length and the results (Shmin orientaon with standard deviaon and breakout length) considering all data. On the right of the stragraphic logs: SHDT log analysed (black line), breakout interval (red line), and breakout orientaons coloured according to different data quality (red = high, green = medium and blue = low) where each bar represents a breakout interval of 50 m maximum length. Map of the surveyed coseismic effects. Sites of measurements are disn- guished between tectonic ruptures and secondary effects (induced by seismic shaking). We report also the sites along faults where no ruptures or other effects were observed. Rose diagrams of the tectonic surface ruptures: A) total data; B) Paganica fault; C) Mt. Bazzano fault and D) Moncchio-Fossa fault. We do not report rose diagrams when the data are less than 5 measurements. Quaternary normal faults are numbered as follow: 1- Paganica, 2 – Poggio Picenze-S. Deme- trio, 3 - Mt. Bazzano, 4 -Moncchio-Fossa, 5- S. Angelo-Tione, 6- Roio-Canetra, 7- Mt. Peno, 8 - Mt. Stabiata, 9- Colle Pracciolo, 10 - Valle del Macchione, 11- Mt. Marine, 12 – Gran Sasso-Mt. Corvo, 13 – Campo Imperatore, 14 – Mt. Laga, 15 – SW Campotosto, 16 – Mt. S. Franco, 17- Mt. Ocre system, 18 – Campo Felice, 19- Ovindoli-Pezza, 20 – Mt. Orbetello (Emergeo Working Group, 2010). Detail of the Paganica surface faulng. Red lines are the mapped rupture strands; the white line is the long-term Paganica fault trace. Photos with white frame show details of the long-term expression and displacements of the Paganica fault. Photos with the red frame show details of the 6 April ruptures (red arrows) when crossing man-made features in the urbanized area (Emergeo Working Group, 2010). Ground ruptures along the Paganica fault. The breaks consist of vercal disloca- ons or warps and open cracks with a persistent orientaon of N130-N140. They cross different type of deposits and type of man-made features, see for instance the main aqueduct in the lower right photo (Emergeo Working Group, 2010). The contribuon of this work is the esmaon of the Shmin along two deep boreholes located close to the 2009 L’Aquila seismic sequence. The results show a Shmin N081 ± 22° and N074 ± 10° oriented for Varoni 1 and Campotosto 1 wells, respecvely, slight different from the mean regional NE–SW apenninic trend. Breakout analysis results show a good agreement with the other available contemporary stress indicators as CMT focal mechanisms (M ≥ 3.9), TDMT focal mechanisms (M ≥ 2.7), σ3 from three recent seismic sequences, Quaternary faults and 2009 coseismic surface ruptures. All data support an ENE acve post-orogenic extension in the area, moreover, the idenficaon of constant Shmin orientaons from 0 down to 15 km depth confirms breakouts as reliable stress indicators also for aseismic areas. The small rotaon of present-day stress field (Shmin) from ~ NE oriented in the southern to ~ ENE in the northern sector, follows the changing trend of the tectonic structures. This orientaon is even more evident northward, up to the 1979 Norcia earthquake area, idenfying a poron of the belt ( ~ 50 km long) with a different Shmin, influenced by the presence of ~ N–S tectonic structure. Differently, the tectonic structures do not seem influence the acve stress field orientaon either northward (1997 Colfiorito earthquake) or southward (1915 Fucino earthquake). Noteworthy, although we have analysed only two boreholes, the results agree with the other stress indicators highlighng that breakouts are reliable indicators of the regional stress field. Seismotectonic sketch showing Shmin orientaons from earthquake data M≥5.4 (Montone et al., 2004) and from borehole breakouts of Campotosto (C1) and Varoni (V1) wells. Main thrust and Quaternary/acve normal faults modified aſter Pizzi & Galadini (2009). The Mw 6.3 mainshock on April 6, 2009 produced deformaon at surface. The most significant ruptures occurred along the SW-dipping, Paganica normal fault (east of L’Aquila), with a clear expression for a connuous extent of about 3 Km (Emergeo Working Group, 2010). THE COSEISMIC EFFECT OF L’AQUILA EVENT PRESENT-DAY STRESS ANALYSIS L’AQUILA APRIL 6 2009 EARTHQUAKE CONCLUSIONS On April 6 2009 a strong earthquake (Mw= 6.3) occurred in Central Italy destroying the old town of L’Aquila and causing the death of hundreds of people. The mainshock was followed by two major aſtershocks on 7 April (Mw= 5.6) and 9 April (Mw= 5.4) and more than 30000 minor events, ~ 170 with Ml> 3.0, during the following two months. The seis- mic sequence is confined in the upper 10 km, with excepon of 7 April earthquake located at 15 km depth. The focal mechanisms of the main events show NW-normal faulng, consistent with the NE-SW trending extensional regime of the central Apennines. The earthquake occurred along the SW-dipping Paganica fault, and produced a surface rupture ~ 3 km long and maximum 10 cm high. Nevertheless, the cumulated size of the Paganica fault scarp and those of other acve faults in the area, sug- gest that the Paganica fault could rupture with larger magnitude earth- quakes than the 2009 event. Thus, although this earthquake caused loss of lives and major damage it does not fully reflect the seismic hazard of the area. We have analyzed in detail the only two deep boreholes of the area to infer the present-day horizontal stress orientaon and dis- criminate regional and local sources of stress. We have compared stress orientaon from borehole breakout data with those deduced from focal mechanism soluons and acve faults to fully depict the stress paern from surface to focal depths. Notwithstanding the results are comparable with the well-known regional present-day stress trend, they reveal a more complex paern, that is probably due to the pres- ence of acve structures diff erently oriented with respect to the aver- age regional trend. ABSTRACT [email protected] [email protected] [email protected] Present-day stress in the area of L’Aquila April 6 2009 earthquake (Italy) ISRSV 04-037 Mariucci M.T., Pierdominici S. , Montone P. INGV - Sezione Sismologia e Teonofisica (Rome, Italy) N African Plate European Plat e I T A L Y
Transcript of Present-day stress in the area of L’Aquila April 6 2009 ...42°N 07Km N 2009 L’Aquila sequence...
MORE INFO IN:MARIUCCI M.T., MONTONE P., PIERDOMINICI S. (2010)- Present-day stress in the surroundings of 2009 L’Aquila seismic sequence (Italy). Geophysical Journal International, on-line July 2010, doi: 10.1111/j.1365-246X.2010.04679.x.
Boncio P. et al. (2004). Ann. Geophys., 47, 1723–1742Centamore E. et al. (1991). Studi Geologici Camerti, Spec. Vol. CROP 11, 1991/2, 125–131Chiarabba C. et al. (2009). Geophys. Res. Lett., 36, L18308, doi:101029/2009GL039627CPTI Working Group (2004), http://emidius.mi.ingv.it/CPTIEmergeo Working Group (2010). Terra Nova, 22, 43–51, doi: 10.1111/j.1365-3121.2009.00915.xhttp://www.eas.slu.edu/Earthquake Center/MECH.IT/ISIDe, http://iside.rm.ingv.it/iside/standard/index.jspMontone P. et al. (2004). J. Geophys. Res., 109(B10410), doi: 10.1029/2003JB002703Pizzi A. & Galadini F. (2009). Tectonophysics, 476(1–2), 304–319, doi:10.1016/j.tecto.2009.03.018Pondrelli S. et al. (2010). Geophys. J. Int., 180, 238–242, doi:10.1111/j.1365-246X.2009.04418.x
Many thanks are due to ENI S.p.A. to provide the borehole data. This work was carried out in the frame of the MIUR-FIRB Project ‘Research and Development of New Technologies for Projection and Defense of Territory fromNatural Risks’ (WP-C3, coordinator Paola Montone).
Acknowledgments
References
Valnerina thrust
Olevano-AntrodocoSibillini thrust
Sangro-Volturno
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Laga Fault
Mt. Bove
Gran Sasso thrustPaganicaFault
Colfiorito
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Shmin from earthquakes
Shmin from borehole breakouts
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43°N
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Projection UTM Zone 33 - Datum WGS 1984
tectonic rupture
secondary effect
no coseismic effect
Quaternary normal fault
LEGEND
0 4 8Km
A-186 measures, 77 max
107 measures, 56 maxB-
32 measures, 12 maxD-
7 measures, 2 maxC-
all data
1
2
7
3
46
89
10
12
13
14
15
16
17
18
19
20
5
11
bohboh
Campotosto
Lake
0 2.5Km
N
Cittareale
MonterealeBorbona
Amatrice
Accumoli
Quaternary deposits
“Laga” Fm., clayey-arenaceous member (lower Messinian)
Normal fault
Thrust fault
Focal mechanism solution
“Maiolica” limestone and “Diaspri”(lower Cretaceous-Dogger)
“Fucoidi” marls (Albian-Aptian)
“Scaglia” marly limestone (Eocene-upper Cretaceous)
“Laga” Fm. , arenaceous-clayey member (lower Messinian)
“Laga” Fm. , arenaceous member (lower Messinian)
“Orbulina” or “Pteropodi” marls (Messinian-Tortonian)
“Cerrogna” marls (upper-middle Miocene)
Shmin orientation
a)
V1
C1
Ol e
va
no
- An
t ro
do
co
th
r us
t
M t . G o r z a n o
CampotostoLake
GRAN SASSOL’AQUILA
Mw5.4
Mw5.5
Mw6.3
b)
Shmin= N081 + 22°L= 962 m
Shmin= N074 + 10°L= 43 m
“Laga”(lower Messinian)Marl units(Tortonian - Langhian)
“Massiccio”(lower Lias)
“Dolomites” (middle - lower Triassic)
Rose Plot log analysed
Breakout intervalBreakoutorientation
“Scaglia”(Oligocene - upper Cretaceous)
“Maiolica” and “Diaspri”(lower Cretaceous - middle Lias)
2000
0 m
1000
3000
4000
5000
6000
V 1 C 1g.l. 1160 m a.s.l. g.l. 1525 m a.s.l. "/
1915
1904
1762
1950
1703
1703
1730
1979
1461
1639
1599
1349
09/04/23 21:49Mw 4.3
09/04/23 14:14Mw 4.1
09/04/07 17:47Mw 5.5
09/04/08 04:27Mw 4.0
09/04/09 03:15Mw 4.4
09/04/06 07:17Mw 4.2
09/04/06 01:32Mw 6.3
09/03/30Mw 4.4
09/07/12 08:38Mw 4.3
09/04/07 09:26Mw 5.1
09/04/05 20:48Mw 4.2
09/04/06 16:38Mw 4.4
09/04/06 03:56Mw 4.5
09/04/07 21:34Mw 4.5
09/04/06 02:37Mw 5.1
09/04/09 04:32Mw 4.3
09/06/22 20:58Mw 4.7
09/04/06 23:15Mw 5.1
09/04/10 03:22Mw 3.9
09/04/09 00:52Mw 5.4
09/07/03 11:03Mw 4.1
09/04/14 20:14Mw 4.0
09/04/13 21:14Mw 5.0
09/04/09 19:38Mw 5.2
09/04/08 22:56Mw 4.1
09/04/15 22:53Mw 4.1
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"/L’AQUILA
Barete
Cittareale
Montereale
Pizzoli
ScoppitoRieti Paganica
Fossa
Tornimparte
Barisciano
Ovindoli
Avezzano
G R A N S A S S O
V1
C1
13.5°E13°E
42°N
0 7Km
N
2009 L’Aquila sequence
Mainshocks
Focal mechanism
solutions
Wells
M<3.03.0<M<3.5
3.5<M<4.5
4.5<M<5.0
M>5.0
ForeshocksMl<3.03.0<Ml<3.5
Ml>3.5
Historical earthquakes
M>5.5
V1
C1
Campo Imperatore
G r a n S a s s o
a)
Ant
rodo
co
Ole
van
o
A
B
C
0 10Km
N
186 coseismic rupture orientations
N
Depth (km)
Mw
00
5 10 15 20
20406080100
120140160
180
Azi
mut
hA
zim
uth
0
5
10
15
20
25
30
35
0 10 110 120 130 140 150 160 170 18020 30 40 50 60 70 80 90 100
Num
ber
Azimuth
b)
c)
V1 σ3C1
C
0
20
40
60
80
100
120
140
160
180
0 1 2 3 4 5 6 7
d)
B AT-axis 2009 L’Aquilasequence:
Shmin-breakoutorientation
Active Fault
Thrust FaultMw>5.2
3.0<Mw<4.0
2.7<Mw<3.0
CMT solution
4.0<Mw<5.2
σ3 from pastsequences
13.5°E
42.4
°N
L’AQUILA
Montereale
Amatrice
Pizzoli
Paganica
FossaTornimparte
Barisciano
Raiale stream
Tempera
Paganica
13.48° E
13.48° E
13.47° E
13.47° E
42.3
7° N
0 250 500125Meters
Fossa
PianolaBazzano
Paganica
L'Aquila
MonticchioPoggioPicenze
Poggio di Roio
Collebrincioni
Aqueduct
L’Aquila 2009 seismic sequence (Chiarabba et al., 2009) with focal mechanism solutions of the main events (Pondrelli et al., 2010). Red circles are the three mainshocks; light blue circles are the foreshocks of the sequence (http://iside.rm.ingv.it/); yellow squares represent the historical seismicity with M ≥ 5.5 (CPTI Working Group 2004); yellow stars are the well locations.
Seismotectonic setting of the area. (a) 170 TDMT T-axis orientations of the 2009 L’Aquila sequence (http://www.eas.slu.edu/Earthquake Center/MECH.IT/); CMT focal mechanisms of the three mainshocks (A, B, C; Pondrelli et al., 2010); σ3 orientation from the 1992, 1994 and 1996 seismic sequences (Boncio et al., 2004); the Shmin orientation inferred from breakout analysis in the two deep wells Campotosto (C1) and Varoni (V1) and the major active normal and thrust faults. In the inset: the rose plot shows the orientation of the 186 coseismic rup-tures identified at surface (Emergeo Working Group, 2010). (b) Azimuth frequency histogram of TDMT T-axis orientations; the red lines represent the T-axis orientations from CMT data of main events (Pondrelli et al., 2010). (c) TDMT T-axis azimuth distribution versus depth together with the Shmin orientation from boreholes breakouts (yellow stars) and the σ3 from the past sequences (red circle). (d) TDMT T-axis versus their magnitude.
(a) Geological and structural map of the study area (redrawn after Centamore et al., 1991) with Shmin orientations from breakout analysis. The inset shows the location and the focal mechanisms of the three 2009 mainshocks.(b) Stratigraphic sketch and breakout analysis of the Varoni 1 (V1) and Campotosto 1 (C1) wells. The two rose plots show breakout orientations scaled for length and the results (Shmin orientation with standard deviation and breakout length) considering all data. On the right of the stratigraphic logs: SHDT log analysed (black line), breakout interval (red line), and breakout orientations coloured according to different data quality (red = high, green = medium and blue = low) where each bar represents a breakout interval of 50 m maximum length.
Map of the surveyed coseismic effects. Sites of measurements are distin-guished between tectonic ruptures and secondary effects (induced by seismic shaking). We report also the sites along faults where no ruptures or other effects were observed. Rose diagrams of the tectonic surface ruptures: A) total data; B) Paganica fault; C) Mt. Bazzano fault and D) Monticchio-Fossa fault. We do not report rose diagrams when the data are less than 5 measurements. Quaternary normal faults are numbered as follow: 1- Paganica, 2 – Poggio Picenze-S. Deme-trio, 3 - Mt. Bazzano, 4 -Monticchio-Fossa, 5- S. Angelo-Tione, 6- Roio-Canetra, 7- Mt. Pettino, 8 - Mt. Stabiata, 9- Colle Praticciolo, 10 - Valle del Macchione, 11- Mt. Marine, 12 – Gran Sasso-Mt. Corvo, 13 – Campo Imperatore, 14 – Mt. Laga, 15 – SW Campotosto, 16 – Mt. S. Franco, 17- Mt. Ocre system, 18 – Campo Felice, 19- Ovindoli-Pezza, 20 – Mt. Orbetello (Emergeo Working Group, 2010).
Detail of the Paganica surface faulting. Red lines are the mapped rupture strands; the white line is the long-term Paganica fault trace. Photos with white frame show details of the long-term expression and displacements of the Paganica fault. Photos with the red frame show details of the 6 April ruptures (red arrows) when crossing man-made features in the urbanized area (Emergeo Working Group, 2010).
Ground ruptures along the Paganica fault. The breaks consist of vertical disloca-tions or warps and open cracks with a persistent orientation of N130-N140. They cross different type of deposits and type of man-made features, see for instance the main aqueduct in the lower right photo (Emergeo Working Group, 2010).
The contribution of this work is the estimation of the Shmin along two deep boreholes located close to the 2009 L’Aquila seismic sequence. The results show a Shmin N081 ± 22° and N074 ± 10° oriented for Varoni 1 and Campotosto 1 wells, respectively, slight different from the mean regional NE–SW apenninic trend. Breakout analysis results show a good agreement with the other available contemporary stress indicators as CMT focal mechanisms (M ≥ 3.9), TDMT focal mechanisms (M ≥ 2.7), σ3 from three recent seismic sequences, Quaternary faults and 2009 coseismic surface ruptures. All data support an ENE active post-orogenic extension in the area, moreover, the identification of constant Shmin orientations from 0 down to 15 km depth confirms breakouts as reliable stress indicators also for aseismic areas. The small rotation of present-day stress field (Shmin) from ~NE oriented in the southern to ~ENE in the northern sector, follows the changing trend of the tectonic structures. This orientation is even more evident northward, up to the 1979 Norcia earthquake area, identifying a portion of the belt (~50 km long) with a different Shmin, influenced by the presence of ~N–S tectonic structure. Differently, the tectonic structures do not seem influence the active stress field orientation either northward (1997 Colfiorito earthquake) or southward (1915 Fucino earthquake). Noteworthy, although we have analysed only two boreholes, the results agree with the other stress indicators highlighting that breakouts are reliable indicators of the regional stress field.
Seismotectonic sketch showing Shmin orientations from earthquake data M≥5.4 (Montone et al., 2004) and from borehole breakouts of Campotosto (C1) and Varoni (V1) wells. Main thrust and Quaternary/active normal faults modified after Pizzi & Galadini (2009).
The Mw 6.3 mainshock on April 6, 2009 produced deformation at surface. The most significant ruptures occurred along the SW-dipping, Paganica normal fault (east of L’Aquila), with a clear expression for a continuous extent of about 3 Km (Emergeo Working Group, 2010).
THE
COSE
ISM
IC E
FFEC
T O
F L’A
QU
ILA
EV
ENT
PRES
ENT-
DAY
STR
ESS
AN
ALY
SIS
L’AQ
UIL
A A
PRIL
6 2
009
EART
HQ
UA
KE
CONCLUSIONS
On April 6 2009 a strong earthquake (Mw= 6.3) occurred in Central Italy
destroying the old town of L’Aquila and causing the death of hundreds
of people. The mainshock was followed by two major aftershocks on 7
April (Mw= 5.6) and 9 April (Mw= 5.4) and more than 30000 minor
events, ~170 with Ml> 3.0, during the following two months. The seis-
mic sequence is confined in the upper 10 km, with exception of 7 April
earthquake located at 15 km depth. The focal mechanisms of the main
events show NW-normal faulting, consistent with the NE-SW trending
extensional regime of the central Apennines. The earthquake occurred
along the SW-dipping Paganica fault, and produced a surface rupture ~3
km long and maximum 10 cm high. Nevertheless, the cumulated size of
the Paganica fault scarp and those of other active faults in the area, sug-
gest that the Paganica fault could rupture with larger magnitude earth-
quakes than the 2009 event. Thus, although this earthquake caused loss
of lives and major damage it does not fully reflect the seismic hazard of
the area. We have analyzed in detail the only two deep boreholes of
the area to infer the present-day horizontal stress orientation and dis-
criminate regional and local sources of stress. We have compared
stress orientation from borehole breakout data with those deduced
from focal mechanism solutions and active faults to fully depict the
stress pattern from surface to focal depths. Notwithstanding the results
are comparable with the well-known regional present-day stress trend,
they reveal a more complex pattern, that is probably due to the pres-
ence of active structures differently oriented with respect to the aver-
age regional trend.
ABSTRACT
[email protected]@ingv.it
Present-day stress in the area of L’Aquila April 6 2009 earthquake (Italy) ISRSV04-037
Mariucci M.T., Pierdominici S., Montone P.INGV - Sezione Sismologia e Tettonofisica (Rome, Italy)
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