23 MAGGIO - V UN AGGIORNAMENTO DEGLI I E C … · 2008)” there is not distinction between Earthquake Fault Zones and Fault Setbacks and general criteria in defining the shape and

Faglie attive e capaci Active and capable faults

P. Boncio Università “G. d’Annunzio” di Chieti-Pescara (Ud’A) [email protected]

G. d’Annunzio Chieti-Pescara

23 MAGGIO - VERSO UN AGGIORNAMENTO DEGLI INDIRIZZI E CRITERI PER LA MICROZONAZIONE SISMICA

Faglia attiva e capace

Faglia per la quale esistono evidenze di ripetuta riattivazione negli ultimi 40.000 anni (parte alta del Pleistocene superiore - Olocene) e capace di rompere la superficie topografica.

Active and capable fault

Fault with evidence of repeated reactivation during the last 40,000

years (upper part of Late Pleistocene - Holocene) and capable of rupturing the ground surface.

Definition in “Indirizi e Criteri per la Microzonazione Sismica 2008”

Boncio et al. – Surface Fault Rupture Hazard (SFRH) Zoning

Active normal fault

In Italy… … it is known that some existing buildings

or critical facilities are exposed to Surface Fault-Rupture Hazard.

The 2009 L’Aquila earthquake (M 6.3) in central Italy brought back to the attention this still unsolved problem in Italian regulations.

Why a PROBLEM ?

7.11.3.1 Local seismic response 7.11.3.2 Stratigraphic amplification 7.11.3.3 Topographic amplification 7.11.3.4 Liquefaction 7.11.3.5 Slope stability

“Norme tecniche per le costruzioni”

(NTC 08)

D.M. 14 gennaio 2008 (G.U. n. 29 del 4.02.2008 suppl.

ord. n° 30)

The Italian regulations

… and the SFRH ??

Legend of:

“Carta delle microzone omogenee in prospettiva sismica (LIVELLO 1)”

“ … only active and capable faults recognized by experts (e.g., in scientific publications).”

Working Group MS, 2008

Why a PROBLEM ?

Norcia case study

(Galli et al., 2005; Gruppo di Lavoro MS Norcia, 2006)

Working Group MS, 2008

Why a PROBLEM ?

A “reference” document for Surface Fault-Rupture Hazard

Since 1972, last revision 2007

• Main purpose: prevent the construction of buildings for human occupancy on the surface trace of active faults.

• Local agencies must regulate most development projects (new or renewed constructions) within the zones. Before a project can be permitted, cities and counties must require a geologic investigation to demonstrate that proposed buildings will not be constructed across active faults.

• If an active fault is found, a structure for human occupancy must be SET BACK from the fault, generally 50 feet (15 m), unless proven otherwise.

• The A-P EFZ Act requires the State Geologist to establish regulatory zones around the surface traces of active faults (Earthquake Fault Zones).

EFZ

• The EFZs vary in width.

The boundaries are placed 150-200 m away from traces of major active faults;

60 to 90 m away from well-defined, minor faults.

Exceptions exist where faults are complex or not vertical.

Problems

• The national regulations (i.e. NTC08) lack of specific recommendations against Surface Fault-Rupture Hazard. • In “Indirizzi e Criteri per la MS (Working Group MS, 2008)” there is not distinction between Earthquake Fault Zones and Fault Setbacks and general criteria in defining the shape and width of the zones are not explicated.

State of the art in ITALY

Towards an improvement of “Indirizzi e Criteri per la Microzonazione Sismica”

Data from world-wide normal faulting earthquakes Earthquake M Fault Kinematics SRL (km) MD (m) WRZ (m) source Notes %SRL HW, ≤150 %SRL HW, ≤40 %SRL FW

1915 Avezzano, Italy

7.0 Fucino system N 36 1.0(v) 1* - 5 (1); 1* - 40 (2)

GG99 (1) Measured in paleoseismological trenches. (2) Measured at the surface. 100 100 0

1915 Pleasant Valley, USA 7.6

China Mt., Tobin, Pearce, Sou Hills N 59 5.8(v)

1* - 195 (mostly ≤ 120) (1);

750 - 1350 (2)Wa84

(1) SR along the main range-front faults. Three local FW splays 115-to-670 m-long, distant up to 50-135 m from MF (Pearce fault). (2) Broad discontinuous zone of SRs parallel to MF (Pearce fault), 4.5 km-long, in the stepover zone betw een Pearce and Sou Hills faults (separation betw een faults = 2.5-to-5 km).

98.0 (calculated for (1)) 90.6 2.2

1946 Ancash, Peru 6.8 Quiches N 21 3.5(v) 1* - 70 Be91WRZ is calculated for the 5.5 km-long Llamacorral segment on a ~1:43,500 tectonic map and a ~1:3,700 map (Fig. 2 in Be91). Local FW splay, 145 m-long, distant up to 25-30 m from MF (central part of the segment).

100 94.2 2.6

1950 Fort Sage Mts., USA 5.6 Fort Sage Mts. N 8.85 0.2(v) 1* - 380 Gi57 Large WRZ (280-to-380 m) due to a 360 m-long (4.1% of SRL) antithetic HW

splay. 95.9 95.9 0

Fairview Peak NR to RN 31.6 3.8(v) 2.9(h) 1* - 1010 (mostly ≤ 150)

Ca96

WRZ > 150 m for 6.6 km (20.9% of SRL) along left-stepping and right-steping bifurcations from MF at the "Bell Canyon salient" (major geometric complexity of MF) and at the "US Highw ay 50" left-stepping and parallel segments; tw o local FW splays 170-to-270 m long, distant up to 305 m from MF.

79.1 70.2 1.4

West Gate N to RN 10 1.1(v) 1.2(h) 1* - 85 Ca96

Tw o parallel ruptures, separated by 220-270 m, overlapping for 395 m, at the souther termination of the main rupture zone. It is unclear w hich one is the MF (possible FW splay?). Probably, partial reactivation of the stepover zone betw een tw o major left-stepping segments.

100 95.7 0(?)

Louderback Mts. RN 14 0.8(v) 1.7(h)

1* - 120 Ca96

Discontinuous ruptures, mostly along left-stepping en echelon segments; overlapping zones betw een adjacent segments (separation ranging from 140 to 195 m) are not considered in calculating WRZ; WRZ is calculated for each segment.

100 98.4 0

Gold king N 8.5 1.0(v)1* - 40 Ca96

Discontinuous ruptures; overlapping zones betw een en echelon segments (separation ranging from 305 to 625 m) are not considered in calculating WRZ; WRZ is calculated for each segment.

100 100 0

Phillips Wash LN 6.2 0.5(v) 0.8(h)1* - 580 Ca96

Discontinuous complex ruptures along right-stepping en echelon and/or parallel segments; maximum WRZ (580 m) for 1.4 km-long system of 3 parallel segments (central part of SR zone).

56.4 53.6 0

1954 Dixie Valley, USA 6.8 Dixie Valley N 42 2.8(v)

1* - 400 (mostly ≤ 120) (1); 1* - 705 (2)

Ca96

(1) SR along the main range-front fault: WRZ > 120 m only for 2.28 km (5.4 % of SRL) along left-stepping bifurcations from MF near "The Bend" (major geometric complexity of MF; i.e.,relay zone betw een northern and southern Dixie V. segments) and at the southern termination of the MF; tw o local FW splays 285-to-320 m long, distant up to 140-260 m from MF near "The Bend". (2) Broad discontinuous zone of SR on the piedmont of "The Bend" area (i.e., major geometric complexity of MF).

95.6 (calculated for (1)) 92.9 1.4

1959 Hebgen Lake, USA

7.3Hebgen, Red Canyon, West Yellowstone Basin

N 26.5 6.1(v) 1* - 300 (mostly < 130)

Wi62

WRZ > 150 m for 1.24 km (4.7% of SRL) along sharp bend betw een northern and southern segments of the Red Canyon fault (major geometric complexity of MF); three local FW splays 440-to-800 m-long, distant 90-to-780 m from MF (near the bend of Red Canyon fault).

95.3 91.3 6.5

1970 Gediz, Turkey 7.1

Akcaalan, Pinarbasi, Erdogmus, Sazkoy, Muratdag

NL to N 42 2.75(v) 0.8 (h)1* - 285 (mostly

< 130) Ta71

WRZ > 130 m in broad deformation zones at lateral terminations of major fault segments (bifurcations from MF, systems of en echelon fractures). One HW splay, 175 m-long, distant 170-to-210 m from MF (Akcaalan segment). Local FW splays, 170-to-190 m-long, distant 30-to-55 m from MF (Akcaalan segment).

98.4 89.9 1.3

1975 Oroville, USA 5.9 Cleveland Hill N to NR 3.8 0.55(v) 1* - 450 (1); 1* - 30 (2)

Cl76

(1) Large WRZ (260-to-450 m) results from overlapping of tw o right-stepping major fault segments (a w estern segment, formed by the south and northw est colinear breaks of Cl76, and an eastern segment, formed by the northeast break of Cl76). (2) WRZ measured individually for the tw o right-stepping segments. Local short footw all crack, ~60 m-long, distant ~30 m from MF (south break).

35.5 (1); 100 (2) 35.5 (1); 100 (2) 1.6

1980 Irpinia, Italy 6.9 Irpinia N 30 1.3(v) 1* - 25 PV90 Measured in paleoseismological trenches. 100 100 0

1981 Corinth, Greece

6.7 Pisia, Shinos N 12-15 1(v) 1* - 70 Pa93, PC04

The Pisia and Shonos rupture zones occurred at or a few meters dow nslope of the MF. Near the foot of an alluvial fan the Shinos rupture zone divided in a series of right-stepping en echelon fractures w ith WRZ of ~70 m.

100 not quantified 0

1983 Borah Peak, USA 7.3 Lost River N to NL 33.3 2.7(v) 1.0(h)

1* - 780 (mostly ≤ 140) Cr87

WRZ > 140 at major geometric complexities of MF (e.g., 1.3 km-long West Spring Block, southern section of MF, WRZ up to 780 m) and at a ~1.7 km-long HW graben, partially reactivated in 1983, up to 240 m-w ide (northern section, Gooseberry Creek). Local FW splay, 740 m-long, distant up to 120 m from MF (southern section, site E of Cr87).

92.3 82.5 2.2

1986 Kalamata, Greece

5.8 Kalamata N 6 0.18(v) 1* - 60 Ly88 Detailed description laking; maximum WRZ obtained from 1:59,000 tectonic map (Fig. 2b of Ly88). 100 ~95 0

1987 Edgecumbe, New Zealand 6.3

Edgecumbe, Onepu, Rotoitipakau (pre-existing) and Aw aiti, Otakiri, Te Teko, Omeheu (new )

N21.7 (1); 16.3 (2) 2.5(v) 1* - 80 Be89

(1) obtained by summing the length of each individual fault; (2) length of the system along the average strike. WRZ exceeds 40 m only at 5 sites along the Edgecumbe fault.

100not quantified

(>98) 0

1995 West Macedonia

6.6 Aliakmon River N 30 0.18(v) 1* - 70 Ch98, Mo98

WRZ from 1:4,000 map in Fig. 2 of Ch98 (only part of SRL); surface ruptures coinciding w ith or very close to pre-existing MF scarps.

1995 Egion, Greece

6.2 Egion N 7.2 0.03(v) 1* - 60 KD96 En echelon ruptures at the w estern termination of MF; separation betw een segments from 80 to 150 m. 100 not quantified 0

2006 Machaze, Mozambique 7.0 Machaze NL (1)

>15 (30-40) 2.05(v) 0.7(h) 1* - 140 (2) FB06

WRZ from ~1:10,000 maps in Fig. 3 of FB06 (only part of SRL); (1) fault is draw n w ith dextral component on map, but is said left in the text and photo; (2) maximum value in the northern strands.

100

2009 L'Aquila, Italy 6.3 Paganica, San Gregorio

N 13 0.12(v) 1* - 140 this paperMost constrained data along the Paganica fault. 100 98.7 (Paganica) 0

1954 Fairview Peak, USA 7.2

not quantified

not quantified

Borah Peak 1983 M 7.3 Crone et al., 1987 BSSA

Main fault

FW splay

Width of the Rupture Zone (WRZ)

18 earthquakes M = 5.6 – 7.6 Kinematics = normal or normal-oblique

Data from world-wide normal faulting earthquakes

For simple fault traces, without major complexities: • WRZ mostly ≤ 120-150 m;

• >95% of SRL with ruptures in the HW within 150 m from MF trace;

• >80-90% of SRL with ruptures in the HW within 40 m from MF trace;

• FW splays are not systematic features: absent or <1.5-2.5% of SRL.

Zoning Surface Fault-Rupture Hazard along normal faults

Boncio et al., 2012 BSSA

Verso un aggiornamento degli Indirizzi e Criteri per la Microzonazione Sismica

Roma, aprile 2013







Livello 1 di MS

NB: La ZAFAC rimanda obbligatoriamente al Livello 3


Livello 1 di MS


Livello 3 di MS


Livello 3 di MS

ZR e Zl possono essere asimmetriche:


Livello 3 di MS



... lastly • Italy lacks of official maps of active/capable faults. Official maps are required, for example, by the Eurocode 8 – Part 5 in order to build regulatory zones around active faults. Therefore, there is an urgent need of a national-scale OFFICIAL map of active/capable faults.

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Documents

23 MAGGIO - V UN AGGIORNAMENTO DEGLI I E C … · 2008)” there is not distinction between Earthquake Fault Zones and Fault Setbacks and general criteria in defining the shape and