Paolo Marco De Martini

Paleoseismicity of Two Historically Quiescent Faults in Australia: Implications for Fault Behavior in Stable Continental Regions

Paleoseismic studies of two historically aseismic Quaternary faults in Australia confirm that cratonic faults in stable continental regions (SCR) typically have a long-term behavior characterized by episodes of activity separated by quiescent intervals of at least 10,000 and commonly 100,000 years or more. Studies of the approximately 30-km-long Roopena fault in South Australia and the approximately 30-km-long Hyden fault in Western Australia document multiple Quaternary surface-faulting events that are unevenly spaced in time. The episodic clustering of events on cratonic SCR faults may be related to temporal fluctuations of fault-zone fluid pore pressures in a volume of strained crust. The long-term slip rate on cratonic SCR faults is extremely low, so the geomorphic expression of many cratonic SCR faults is subtle, and scarps may be difficult to detect because they are poorly preserved. Both the Roopena and Hyden faults are in areas of limited or no significant seismicity; these and other faults that we have studied indicate that many potentially hazardous SCR faults cannot be recognized solely on the basis of instrumental data or historical earthquakes. Although cratonic SCR faults may appear to be nonhazardous because they have been historically aseismic, those that are favorably oriented for movement in the current stress field can and have produced unexpected damaging earthquakes. Paleoseismic studies of modern and prehistoric SCR faulting events provide the basis for understanding of the long-term behavior of these faults and ultimately contribute to better seismic-hazard assessments.

Paleoseismicity of the 1981 Corinth earthquake fault: Seismic contribution to extensional strain in central Greece and implications for seismic hazard

We present paleoseismological trenching results for the active Skinos Fault, which ruptured the surface on the Alkyonides Gulf basin margin in the 1981 Gulf of Corinth earthquake sequence. Three trenches expose evidence of up to six previous events which are comparable to the 1981 deformation in terms of size and geometry. Vertical displacement produced by the 1981 earthquake ranged from 0.45 to 1.3 m at the Bambakies Fan trench sites, decreasing towards the eastern fault tip east of the trenches. Trench 1 reveals two previous events with vertical displacements between 0.5 and 1.2 m since 390 A.D. Trench 2 reveals five or six previous events, but these are not dated. Trench 3 reveals four previous events since 670 A.D. Vertical displacements associated with interpreted paleoearthquakes at the trench sites are ≤1.2 m. The recurrence interval on the Skinos Fault is estimated to average 330 years. However, significant variation in recurrence interval is allowed by the available radiometric dates. Average vertical displacement rates derived from the trenches are in the range 0.7–2.5 mm/yr. A similar long-term average vertical displacement rate of 1.2–2.3 mm/yr is estimated for the lifespan of the basin-bounding fault. This equates to a horizontal seismic strain contribution of ≤2.5 mm/yr from the Skinos Fault. This local seismic strain rate overlaps, within error, with geodetically determined velocities across the Alkyonides Gulf assumed to represent uniform deep-crustal strain. Thus seismic deformation on the basin-bounding fault system may take up the major part of extension across the basin, and aseismic strain is not necessitated by the data. If correct, this would imply that geodetically determined strain rates may be used as a proxy for potential seismic moment release in seismic hazard analyses for this region.

Discrimination of Tsunami Sources (Earthquake versus Landslide) on the Basis of Historical Data in Eastern Sicily and Southern Calabria

Abstract The source mechanisms responsible for large historical tsunamis that have struck eastern Sicily and southern Calabria are a topic of robust debate. We have compiled a database of historical coeval descriptions of three large tsunamis: 11 January 1693, 6 February 1783, and 28 December 1908. By using accounts of run-up and inundation and employing an approach proposed by Okal and Synolakis in 2004, we can provide discriminants to define the nature of the near-field tsunami sources (fault dislocation or landslide). Historical reports for the 1908 event describe affected localities, maximum run-ups, and inundation areas. However, for the 1693 and 1783 tsunamis, reports are limited to inundation and occasional run-up estimates. We calculate run-up values for these events using available relations between inundation and run-up. We employed the model of Okal and Synolakis to the obtained profiles of tsunami run-up along the inundated shorelines. The 1908 run-up data distribution confirms that the tsunami is compatible with a seismic dislocation source, whereas the 1783 data supports contemporary observations and recent offshore investigations suggesting that the tsunami was produced by an earthquake-triggered submarine landslide. Analysis of the 1693 event data suggests that the tsunami was generated during a tectonic event and thus a seismogenic source should be found offshore.

Late Holocene Earthquakes on the Aeropuerto Fault, Managua, Nicaragua

Managua, capital of Nicaragua, is built on the shore of Lake Managua, within a densely faulted graben at a major discontinuity in the Central American volcanic chain. Shallow moderate earthquakes ( M s 6-6.2) ruptured faults with devastating effect at the heart of urban Managua in 1931 and 1972, and damaging earthquakes are cataloged in the earlier history of the surrounding region. The Aeropuerto fault is a major structure in the Managua Graben, but like other faults in this area its behavior is little understood. Paleoseismic investigations now suggest that the most recent large earthquake on this fault occurred sometime during the interval A.D. 1650-1810. An earlier earthquake on this fault occurred prior to A.D. 1390 and possibly around 2000 B.P. On the basis of stratigraphic correlations we estimate the ages of two shorelines associated with former high stands of Lake Managua to be less than 6.4 ka and approximately 2 ka, respectively. Deformation of these abandoned shorelines adjacent to the Aeropuerto fault implies a vertical slip rate of 0.3 to 0.9 mm/yr. Strike-slip movement on this fault is also expected, but no direct measurement could be performed. By comparison with faults of similar geometry in the Managua area that ruptured in 1931 and 1972, we suspect a left-lateral component of horizontal slip that is higher than the vertical one but less than 5 mm/yr. Additional data on slip rate and timing of paleoearthquakes are needed to better assess the Holocene behavior of the Managua faults and to investigate the influence of magmatic processes on the nature of faulting in the Managua Graben. Manuscript received 15 January 2002.

Sand volcanoes induced by the April 6th 2009 Mw 6.3 L’Aquila earthquake: a case study from the Fossa area

This paper presents the study of some liquefaction features occurred near the Fossa village due to the April 6, 2009, Mw 6.3 L’Aquila earthquake (Central Italy). Our investigation is based on trenching and coring campaigns as well as sedimentological analyses and datings. The geometrical elements of the sand volcanoes on the surface, of the dike used to rise up and of the probable sandy source at depth are presented. A sandy pockets level found at less than 1 m of depth, interpreted as possible evidence for a paleo-liquefaction event is discussed. Sedimentologic and morphoscopic analyses both provided the necessary elements and parameters to link the ca. 4 m deep sandy layers to the 2009 sand blows on the ground surface as well as to the paleo-liquefaction layer and defined the main characteristics of the deposits sealing the sands that experience liquefaction at depth. Finally a tentative correlation between the paleo-liquefaction layer and the 1461 AD or the 1703 AD local earthquakes is suggested based on the available age constraints.

The Contribution of Airborne LiDAR Data to the Assessment of Surface Faulting Hazard for Lifelines Crossing Active Faults: An Example from the Central Apennines, Italy

In case of moderate to strong earthquakes (generally for M > 5.5), coseismic slip along a fault can reach directly the ground surface and produce surface faulting. Although scarcely considered in the Italian legislation, surface faulting hazard can have a relevant societal impact because it exposes to substantial risk urban areas and/or important infrastructures, facilities and critical lifelines that are settled or planned in coincidence of an active and capable fault trace. In this paper we present a case study from the area hit by the Mw 6.1 April 6, 2009 L’Aquila earthquake (Central Italy), where buildings and critical lifelines located across or near the coseismic surface ruptures suffered significant damage. High resolution (1 m) LiDAR topographic data contributed to the assessment of surface faulting hazard through a better imaging of the surface geometrical arrangement of the earthquake causative fault and through the analysis of the spatial relationships between active fault splays and critical lifelines and infrastructures.