The April 2009 L’Aquila earthquake: a retrospective discussion on scientific knowledge
Istituto Nazionale di Geofisica e Vulcanologia
INGV ‐ processoaquila.wordpress.com Outlines
1 What we knew and we did in the years preceding the earthquake
2 What we knew and we did in the months preceding the earthquake
3 What happened between March 29th and April 5th 2009
4 April 6th earthquake: which improvements are needed
5 Forethoughts on the verdict
INGV ‐ processoaquila.wordpress.com What we knew in the years preceding the 1 earthquake
Seismic hazard for the region (Hazard Map updated in 2004
Historical seismicity and active strain indicate high earthquake potential
Probability of occurrence of a M 5+ earthquake was relatively high (≈10-15%)
Vulnerability of several building and historical heritage in L’Aquila city was known [GNDT-LSU, 1999; SIGOIS, 2006]. Amato e Ciaccio 2012 Censimento di vulnerabilità degli edifici pubblici strategici e speciali nelle regioni Abruzzo, Basilicata, Calabria, Campania, Molise, Puglia e Sicilia Orientale.
There were several seismic sequences in the area with main shocks M≅4 not followed by any destructive event (i.e., 1985)
INGV ‐ processoaquila.wordpress.com The seismic hazard Map 1 The seismic hazard map of Italy (2004)
L’Aquila has been classified as an high seismic hazard region after the 1915 Avezzano earthquake. All the houses built after that date should take into account the seismic code.
INGV ‐ processoaquila.wordpress.com Medium-long term probability models of 1 occurence of a M>5 earthquake
Different models [Pace et al., 2006; Faenza et al., 2003; Cinti et al., 2006] gave a probability of occurrence of about 10%-15% in 10- 50 years
Seismogenic region used in the probability evaluations (dark colors are higher probability. INGV ‐ processoaquila.wordpress.com Medium-long term probability models of 1 occurence of a M>5 earthquake
Boschi et al. (1995 BSSA) find that the probability of an earthquake of magnitude greater than or equal to 5.9 in this area is always 1.00 (100%), regardless of the time window of estimates (5, 20 and 100 years). They are explain the statistics are not reliable in this case (*) (*) In Boschi et al. (1995) statistical computation focuses on a very small area (zone 34), which includes the region of L'Aquila and only 3 historical earthquakes. All zoning later used for similar studies, such as for the national hazard map (http://zonesismiche.mi.ingv.it/) have used larger areas to include more data and to have more robust Seismogenic regions used in statistics (see figure on the right and on the probability evaluations of previous slide). Boschi et al.,1995 INGV ‐ processoaquila.wordpress.com Interseismic strain inferred from GPS 1 Strain Rate Velocity field
Normal faulting Schematic geological section across the M. D’Ocre – Gran Sasso structures (after Satolli and Calamita 2008)
INGV ‐ processoaquila.wordpress.com We did all we could do! 1
Scientists provided results and products to assess seismic hazard and vulnerability of the Italian territory
The Italian Civil Protection committed many of these research activities
Updated seismic hazard map and building code became an official law of the Italian Government
The seismic monitoring and surveillance of the Italian territory guaranteed real-time information to National and local authorities
INGV ‐ processoaquila.wordpress.com 1 In the years preceding the earthquake
There were a good synergy between scientific community and national governmental agencies
Information was delivered to local authorities
Scientific results were available on websites (at least the most important)
BUT
Preparedness of society was (/ is) rather poor
Resilience of society was (/ is) extremely scarce
In Abruzzo there was a project 2007 with schools described in the movie “Non chiamarmi terremoto”
http://www.nonchiamarmiterremoto.it/Non_chiamarmi_terremoto/home.html
Indeed , other outreach activities were (/ are) not enough targeted. INGV ‐ processoaquila.wordpress.com What we knew in the months 2 preceding the earthquake
On December 2008 a seismic sequence began near the L’Aquila area, well-known for its high seismic risk. Seismicity occurred also near Sulmona (about 60 km southern of L’Aquila)
The seismicity had a similar pattern to other sequences occurred in the area (the most recent were in 1985 M 4.2, 1994 M 3.9 and 1996 M 4.1)
The evolution of seismic activity was followed in real time at INGV and communicated to the Civil Protection Department
INGV ‐ processoaquila.wordpress.com Seismicity in the months preceding the 2 earthquake
Seismicity map of the region in the months preceding the earthquake.
On December 2008 a seismic sequence began near the L’Aquila area, well- known for its high seismic risk. Seismicity occurred also near Sulmona.
INGV ‐ processoaquila.wordpress.com What happened between 3 March 29th and April 5th
On March 29th G. Giuliani, a technician at the Gran Sasso National Laboratory, (INFN) predicts (again) and broadcasts the occurrence of a large magnitude event in Sulmona (60 km far away from L’Aquila). He relied on indirect measures of radon emission.
The rate of earthquakes increased on March 30th 2009 after a
ML 4.1 earthquake that struck the L’Aquila area
Preoccupation and panic in population raised
On March 31st the Italian Civil Protection organize in L’Aquila a meeting of the Commissione Grandi Rischi, an expert group that advises the Civil Protection agency on the risks of natural disasters
INGV ‐ processoaquila.wordpress.com The RADON precursor: Prediction claim 3
Prediction claim by Giampaolo Giuliani (Laboratori Nazionali del Gran Sasso) based on radon emission
Broadcasted March 29th : “Earthquake will happen in 6-24 hours in the region: of Sulmona”
Example of prediction: More than 15 peaks in 3 days; Two events (white labels) of moderate magnitude claimed to be predicted; No correlation between amplitude of the peaks and e arthquakes.
INGV ‐ processoaquila.wordpress.com Earthquakes in time 3 3 From January to the end of March 2009 the number of earthquakes was quite constant. Seismicity increased after the M=4.1 earthquake as results of its aftershocks (red empty box). The number of events increased after the occurrence on the April 6th event (red area) INGV ‐ processoaquila.wordpress.com Space-time evolution of seismicity 3 Seismicity in the NW-SE area centered on the mainshock epicenter
IN the months preceding the 6 of April 2009, the seismic sequence was concentrated in few km (red box indicates the seismicity after the M=4.1 earthquake)
January April
INGV ‐ processoaquila.wordpress.com The foreshocks sequence 3
(Chiaraluce et al., 2011)
Relocation of the foreshocks show that the seismicity following the M=4 earthquake (purple circles) was on a fault N-S oriented, not the same one that would rupture on April 6th (black star and dots in the upper AA’ section)
INGV ‐ processoaquila.wordpress.com 3 The seismic sequence was not a certain precursor
In the period 2008-2010 Mele et al. (2010) identify 127 seismic sequences in Italy and verify that nearly 70% of seismicity belongs to sequences, having very different durations and patterns. 1 out of 127 is followed by a destructive event.
A posteriori for the ETAS model - On march 31 the probability of occurrence of a M>5.5 was 0.5%, on April 5th it was 0.05% , that is 5 over 10.000!
The complex spatial pattern of foreshocks further inhibits to make any statement concerning evidence of the nucleation process of a moderate-to-large magnitude earthquake
We can confirm that there were no reasons to say that the sequence of events of low magnitude could be considered a certain precursor of a strong event.
INGV ‐ processoaquila.wordpress.com th April 6 earthquake & aftershocks 4
After the 6 of April, the seismicity spread out for tens of km from the hypocenter
Immediately after the main shock of April 6th INGV experts provided all the available information to the Italian Civil Protection to manage the
INGV ‐ processoaquila.wordpress.com emergency and plan the intervention. April 6th earthquake & aftershocks 4
Migration of seismicity on Campotosto was followed by INGV and communicated to DPC
On April 7th INGV issues its first 24-hr aftershock forecast (ETAS) at 8:00 am, about 15 hrs after
INGV ‐ processoaquila.wordpress.com Lessons from the earthquake 4
Many scientific papers studied the seismic sequence finding interesting clues on the role of fluids in the seismogenic process, but still there are no reasons to say that the sequence could be considered a certain precursor of a strong event.
This earthquake has left the scientific community and the involved stakeholders lessons concerning the necessary prevention actions, as well as the urgent need to train and educate the society to live in earthquake prone areas.
These lessons should spur all the public authorities towards a better use of seismic hazard maps and available information to reduce vulnerability of the Italian territory. These lessons demand for urgent initiatives to increase the resilience of the Italian society to natural hazards.
INGV ‐ processoaquila.wordpress.com Forethoughts on the verdict
Unfortunately, these lessons are still unheard. The sentence of L’Aquila process goes in a different dangerous direction, indicating that the reduction of the vulnerability is impossible because too expensive.
The responsibility of local authorities and administrators is not discussed and considered: the prosecutor Picuti asked to write off the positions of the head of civil protection Bertolaso and regional assessor Stati.
INGV ‐ processoaquila.wordpress.com