Tsunami hazard and risk evaluation in the Gulf of Naples: State of the art and perspectives S. Tinti, F. Zaniboni, A. Armigliato and G. Pagnoni University of Bologna, Dept. of Physics, Sector of Geophysics, Bologna, ITALY COST Conference on “Urban Habitat Constructions Under Catastrophic Events” 16-18 September 2010 Naples (Italy)
PRESENTATION OUTLINE • Brief overview of the tsunami history of the Gulf of Naples • Tsunami hazard assessment through numerical simulations of historical/scenario tsunamis generated in the near field (Vesuvius, Ischia) and in the far field (Stromboli) • Future perspectives: tsunami vulnerability and risk assessment
HISTORICAL TSUNAMIS IN THE MEDITERRANEAN Catalogue produced as a deliverable of the EC FP6 TRANSFER Project (http://www.transferproject.eu/). Dimension and colour of the symbols indicate different values of tsunami intensity expressed in the Sieberg-Ambraseys scale.
TSUNAMIS IN THE GULF OF NAPLES VESUVIUS NAPLES 2 low-reliability (6 events) 1760 events ISCHIA CAPRI
QUERYING THE DATABASE FOR EVENT PARAMETERS
QUERYING THE DATABASE FOR EVENT DESCRIPTION
Vesuvius is not the only cause of tsunamis in the Gulf of Naples! Near field: Ischia (landslides) Far field: Stromboli (landslides)
TSUNAMI HAZARD ASSOCIATED WITH VESUVIUS PYROCLASTIC FLOWS Reference case: 1631 eruption and tsunami According to Rosi et al. (1993), in the harbour of Naples waves of 2-5 m in amplitude were observed. From the TRANSFER tsunami catalogue, we know that the sea was seen to withdraw and then to inundate the coast of the Gulf for three times: the largest retreat (about 1 mile) was reported in Sorrento.
FORCING From Tinti et al. (2003) based on the hypothesis that the tsunami was due to the light component of the pyroclastic flow (see also Esposti Ongaro et al. (2002)). cm Forcing is assumed to be a pressure impulse propagating seaward with constant radial velocity over a sector centered on the Vesuvius crater. Pulse duration assumed constant. Pulse radial speed: 15 m/s. 10 min 5 min 2 min Dynamic pressure (kPa) Time (min)
TSUNAMI PROPAGATION FIELDS cm Computed by means of the numerical FE code UBO- 30 min 20 min TSUFE, developed and maintained by TRT- DFUNIBO and implementing the non-linear shallow water equations (see Tinti et al., 1994). 10 min 5 min Field of maximum tsunami energy (kJ/m 2 ) in the first 30 minutes after the onset.
MAXIMUM WATER ELEVATION ALONG THE COAST 1-Miseno, 2-Pozzuoli, 3-Bagnoli, 4-Posillipo, 5-Napoli, 6-Torre del Greco, 7-Torre Annunziata, 8-Castellammare, 9-Sorrento, 10-Positano
SENSITIVITY ANALYSIS VARYING PULSE SPEED VARYING PULSE DURATION 1 2 3 7 8 9 10 1 2 3 5 6 9 10 4 5 6 4 7 8 0.6 Extreme water elevations (m) Extreme water elevations (m) 0.4 0.4 0.2 0.2 0.0 0.0 -0.2 -0.2 -0.4 -0.4 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Distance along the coast (km) Distance along the coast (km) V = 10 m/s 1.5 min V = 15 m/s 3.0 min V = 20 m/s 6.0 min V = 25 m/s
TSUNAMI HAZARD ASSOCIATED WITH CATASTROPHIC LANDSLIDES AT ISCHIA
Ischia Debris Avalanche (IDA) • Series of surveys around Ischia from 1998 to 2004 evidenced submarine deposits all around the island (N, W and S) • IDA as a worst case scenario • The largest deposit was located south of Ischia - covering an area of more than 250 km 2 - up to 50 km far from the coast - thickness ranging 5-30 m - volume of 1.5-3 km 3 -dating some ky BP Chiocci F.L., de Alteriis G. (2006) . The Ischia debris avalanche: first clear submarine evidence in the Mediterranean of a volcanic island prehistorical collapse, Terra Nova , 18, 202-209.
LANDSLIDE NUMERICAL MODEL (UBO-BLOCK) • Mass divided into a “chain” of blocks that: - conserve their volume - can interact - can’t separate • Centre of mass model Motion equation i time step a ik = G ik - R ik + F ik k block G ik gravity and bottom friction • Numerical resolution of motion equation R ik resistance term F ik internal interaction term • The simulation is stopped when mass velocity goes below a predefined threshold or when the slide exits the computational domain Tinti S., Bortolucci E., Vannini C., 1997 . A block-based theoretical model suited to gravitational sliding, Natural Hazards, 16, 1-28.
LANDSLIDE SIMULATION • MODEL INPUTS - sliding surface - top of sliding mass - predefined centre of mass trajectory (red line) - lateral slide boundaries
LANDSLIDE SIMULATION initial slide thickness Chiocci F.L., de Alteriis G. (2006) Height (m) Volume ~ 3.7 km 3 Distance along the profile (m)
LANDSLIDE SIMULATION Time step: 1 second Number of blocks: 10 Subaerial friction coefficient ( m a ): 0.09 Submarine friction coefficient ( m w ): 0.02 Density: 2000 kg/m 3 Final simulation time: 710 s
LANDSLIDE SIMULATION Landslide profile • Mass deposits between 900 and 1000 m b.s.l. • runout of about 30 km
LANDSLIDE SIMULATION VELOCITY AND FROUDE NUMBER V hor Fr = √ g ·h
COMPUTED TSUNAMI PROPAGATION FIELDS (UBO-TSUFE code)
MAXIMUM AND MINIMUM WATER ELEVATIONS OVER THE COMPUTATIONAL DOMAIN
TSUNAMI HAZARD ASSOCIATED WITH CATASTROPHIC LANDSLIDES AT STROMBOLI
December 30 th 2002 Tsunamis Photos taken during the January 2003 post-event field survey • Caused by 2 landslides in Sciara del Fuoco • The first submarine, the second sub aerial • Relatively small-sized, volume ~ 10 6 - 10 7 m 3 • Waves reaching 10 m runup, affecting all the coasts of the island
FAR-FIELD TSUNAMI EFFECTS OBSERVATIONS AFTER THE 30 DECEMBER 2002 EVENTS From Maramai et al. (2005) For example, at Marina di Camerota (point 5) a sea withdrawal of about 5 – 12 m was observed. In the zones adjacent to the harbour, seawater penetrated inland for about 60 – 70 m
THE HOLOCENE SCIARA DEL FUOCO COLLAPSE - occurred about 5 ky BP - volume estimated in 1 km 3 - landslide simulated by means of UBO-BLOCK2D (25 blocks, 0.5 s time step) - final simulated run-out distance: 15 km See e.g. Rosi et al. (2000) Tinti et al. (2000, 2003) Tibaldi (2001)
Stromboli Holocene landslide scenario: Snapshots of the tsunami propagation in the southern Tyrrhenian (computed with a finite difference code by Dr. Kenji Satake based on TRT-DFUNIBO landslide simulation)
Extreme water elevation fields computed in the Naples harbour area for the Stromboli Holocene landslide scenario (computed by means of UBO-TSUFD code in the frame of the DPC “Progetto Porti” coordinated by EUCENTRE) Maximum positive elevation field (inundation) Maximum negative elevation field (retreat)
FUTURE PERSPECTIVES: TSUNAMI VULNERABILITY AND RISK ASSESSMENT
The tsunami risk estimation and mitigation problem has been tackled in a systematic way only in very recent years. In general terms, the risk estimation is the result of the combination of detailed inundation maps coming from the hazard analysis, and of the vulnerability assessment. One of the approaches existing for the second aspect has been developed by the EU-funded SCHEMA project: it distinguishes between primary (type and material) and secondary (ground, age, foundation, orientation, etc.) criteria for buildings, and it adopts a building damage matrix, basically depending on building type and water inundation depth. Vulnerability classification established in SCHEMA
Vulnerability classification for selected areas around Catania
Building damage matrix adopted by SCHEMA
CONCLUSIONS The tsunami hazard assessment for the Gulf of Naples has been performed so far exclusively on the base of the scenario technique. Three main different sources of tsunami hazard have been identified in the volcanic activity of Vesuvius and on the possible occurrence of large to catastrophic landslides in correspondence with Ischia and Stromboli. The main threat appears to be related to landslides in Ischia, with the IDA scenario forecasting tsunami waves impacting the Gulf within 10-15 minutes and with maximum elevations in the order of 20 m. Our numerical simulations must be improved as regards the tsunami generation by pyroclastic flows. Tsunami vulnerability and risk assessment is a topic that has only recently started to be tackled. We have briefly described a method that have been proposed by the EC SCHEMA Project, based on the assumption of proper vulnerability and damage matrices, to be crossed with the expected maximum inundation in a given site provided by numerical simulations. We have shown a preliminary application to the city of Catania.
alberto.armigliato@unibo.it http://www.transferproject.eu/ http://www.schemaproject.net /
TSUNAMI MODEL – COMPUTATIONAL GRID Km Km
TSUNAMI SIMULATION MAXIMUM AND MINIMUM WATER ELEVATIONS ON THE COAST Procida Ischia Southern Tyrrhenian coast
TSUNAMI SIMULATION SYNTHETIC MARIGRAMS
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