Influence of near-surface stratigraphy on coastal landslides at Sleeping Bear Dunes National Lakeshore, Lake Michigan, USA

This paper is not subject to U.S. copyright. The definitive version was published in Journal of Coastal Research 20 (2004): 510-522, doi:10.2112/1551-5036(2004)020[0510:IONSOC]2.0.CO;2.Lake-level change and landslides are primary controls on the development of coastal environments along the coast of northeastern Lake Michigan. The late Quaternary geology of Sleeping Bear Dunes National Lakeshore was examined with high-resolution seismic reflection profiles, ground-penetrating radar (GPR), and boreholes. Based on sequence-stratigraphic principles, this study recognizes ten stratigraphic units and three major unconformities that were formed by late Pleistocene glaciation and postglacial lake-level changes. Locally high sediment supply, and reworking by two regressions and a transgression have produced a complex stratigraphy that is prone to episodic failure. In 1995, a large landslide deposited approximately 1 million m3 of sediment on the lake floor. The highly deformed landslide deposits, up to 18 m thick, extend 3–4 km offshore and unconformably overlie well-stratified glacial and lacustrine sediment. The landslide-prone bluff is underlain by channel-fill deposits that are oriented nearly perpendicular to the shoreline. The paleochannels are at least 10 m deep and 400 m wide and probably represent stream incision during a lake-level lowstand about 10.3 ka B.P. The channels filled with sediment during the subsequent transgression and lake-level highstand, which climaxed about 4.5 ka B.P. As lake level fell from the highstand, the formation of beach ridges and sand dunes sealed off the channel and isolated a small inland lake (Glen Lake), which lies 5 m above the level of Lake Michigan and may be a source of piped groundwater. Our hypothesis is that the paleochannels act as conduits for pore water flow, and thereby locally reduce soil strength and promote slope failure.Generous support for this project was provided by Max Holden and Steve Yancho of Sleeping Bear Dunes National Lakeshore

Seismological and geotechnical aspects of the Mw=6.3 l’Aquila earthquake in central Italy on 6 April 2009

The L’Aquila earthquake occurred on April 6 2009 at 03:32:39 local time. The earthquake (Mw=6.3) was located in the central Italy region of Abruzzo. Much of the damage occurred in the capital city of L’Aquila, a city of approximate population 73000, although many small villages in the surrounding region of the middle Aterno river valley were also significantly damaged. In the weeks following the earthquake, the Geo-Engineering Extreme Events Reconnaissance (GEER) international team, comprised of members from different European countries and the U.S., was assembled to provide post-earthquake field reconnaissance. The GEER team focused on the geological, seismological, and geotechnical engineering aspects of the event. We describe the principal seismological findings related to this earthquake including moment tensors of the main shock and two triggered events, the aftershock pattern and its variation with time, tectonic deformations associated with the main shock, surface fault rupture, and the inferred fault rupture plane. We describe damage patterns on a village-to-village scale and on a more local scale within the city of L’Aquila. In many cases the damage patterns imply site effects, as neighbouring villages on rock and soil had significantly different damage intensities (damage more pronounced on softer sediments). The April 6 mainshock was the best-recorded event to date in Italy. We present metadata related to the recording sites and then present preliminary comparisons of the data to GMPEs. Those comparisons support the notion of faster distance attenuation in Italy relative to the average for active regions as reflected in NGA GMPEs. Several incidents of ground failure are then discussed, including a number of rockfalls and minor landslides. Perhaps the most significant incidents of ground failure occurred at Lake Sinizzo, for which we describe a number of slumps and spreads around the lake perimeter. This is documented using field observations as well as LIDAR and bathymetric data

Engineering reconnaissance following the August 24, 2016 M6.0 Central Italy earthquake

An earthquake with a moment magnitude reported as 6.0 from INGV (Istituto Nazionale di Geofisica e Vulcanologia); occurred at 03:36 AM (local time) on 24 August 2016 in the central part of Italy. The epicenter was located at the borders of the Lazio, Abruzzi, Marche and Umbria regions, about 2.5 km north-east of the village of Accumoli and about 100 km from Rome. The hypocentral depth was about 8 km (INGV). We summarize preliminary findings of the Italy-US GEER (Geotechnical Extreme Events Reconnaissance) team, on damage distribution, causative faults, earthquake-induced landslides and rockfalls, building and bridge performance, and ground motion characterization. Our reconnaissance team used multidisciplinary approaches, combining expertise in geology, seismology, geomatics, geotechnical engineering, and structural engineering. Our approach was to combine traditional reconnaissance activities of on-ground recording and mapping of field conditions, with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. We anticipate that results from this study, will be useful for future post-earthquake reconnaissance efforts, and improved emergency respons

Semi-empirical relationships to assess the seismic performance of slopes from an updated version of the Italian seismic database

Funder: Dipartimento della Protezione Civile, Presidenza del Consiglio dei Ministri; doi: http://dx.doi.org/10.13039/100012783; Grant(s): ReLUIS research project - Working Pachage 16: Geotechnical Engineering - Task Group 2: Slope stabilityAbstractSeismic performance of slopes can be assessed through displacement-based procedures where earthquake-induced displacements are usually computed following Newmark-type calculations. These can be adopted to perform a parametric integration of earthquake records to evaluate permanent displacements for different slope characteristics and seismic input properties. Several semi-empirical relationships can be obtained for different purposes: obtaining site-specific displacement hazard curves following a fully-probabilistic approach, to assess the seismic risk associated with the slope; providing semi-empirical models within a deterministic framework, where the seismic-induced permanent displacement is compared with threshold values related to different levels of seismic performance; calibrating the seismic coefficient to be used in pseudo-static calculations, where a safety factor against limit conditions is computed. In this paper, semi-empirical relationships are obtained as a result of a parametric integration of an updated version of the Italian strong-motion database, that, in turn, is described and compared to older versions of the database and to well-known ground motion prediction equations. Permanent displacement is expressed as a function of either ground motion parameters, for a given yield seismic coefficient of the slope, or of both ground motion parameters and the seismic coefficient. The first are meant to be used as a tool to develop site-specific displacement hazard curves, while the last can be used to evaluate earthquake-induced slope displacements, as well as to calibrate the seismic coefficient to be used in a pseudo-static analysis. Influence of the vertical component of seismic motion on these semi-empirical relationships is also assessed.</jats:p

Control of style-of-faulting on spatial pattern of earthquake-triggered landslides

Predictive mapping of susceptibility to earthquake-triggered landslides (ETLs) commonly uses distance to fault as spatial predictor, regardless of style-of-faulting. Here, we examined the hypothesis that the spatial pattern of ETLs is influenced by style-of-faulting based on distance distribution analysis and Fry analysis. The Yingxiu–Beichuan fault (YBF) in China and a huge number of landslides that ruptured and occurred, respectively, during the 2008 Wenchuan earthquake permitted this study because the style-of-faulting along the YBF varied from its southern to northern parts (i.e. mainly thrust-slip in the southern part, oblique-slip in the central part and mainly strike-slip in the northern part). On the YBF hanging-wall, ETLs at 4.4–4.7 and 10.3–11.5 km from the YBF are likely associated with strike- and thrust-slips, respectively. On the southern and central parts of the hanging-wall, ETLs at 7.5–8 km from the YBF are likely associated with oblique-slips. These findings indicate that the spatial pattern of ETLs is influenced by style-of-faulting. Based on knowledge about the style-of-faulting and by using evidential belief functions to create a predictor map based on proximity to faults, we obtained higher landslide prediction accuracy than by using unclassified faults. When distance from unclassified parts of the YBF is used as predictor, the prediction accuracy is 80%; when distance from parts of the YBF, classified according to style-of-faulting, is used as predictor, the prediction accuracy is 93%. Therefore, mapping and classification of faults and proper spatial representation of fault control on occurrence of ETLs are important in predictive mapping of susceptibility to ETLs

CPT-Based Probabilistic Assessment of Seismic Soil Liquefaction Initiation

The correlation of seismic field performance with in situ index test results has been proven to be a reliable method for defining the threshold between liquefaction and non-liquefaction. The objective of this research was to define, in the most accurate and unbiased manner possible, the initiation of seismic soil liquefaction using the cone penetration test (CPT). Contained in this report are the results of this research. Case histories of occurrence and non-occurrence of soil liquefaction were collected from seismic events that occurred over the past three decades. These were carefully processed to develop improved CPT-based correlations for prediction of the likelihood of “triggering,” or initiation, of soil liquefaction during earthquakes. Important advances over previous efforts include (1) Collection of a larger suite of case histories, (2) Development of an improved treatment of CPT thin-layer corrections, (3) Improved treatment of normalization of CPT tip and sleeve resistances for effective overburden stress effects, (4) Improved evaluation of the cyclic stress ratio (CSR) in back-analyses of field case histories, (5) Assessment of uncertainties of all key parameters in back-analyses of field case histories, (6) Evaluation and screening of case histories on the basis of overall uncertainty, and (7) Use of higher-order (Bayesian) regression tools. The resultant correlations provide improved estimates of liquefaction potential, as well as quantified estimates of uncertainty. The new correlations also provide insight regarding adjustment of CPT tip resistance for effects of “fines” content and soil character for purposes of CPT-based liquefaction hazard assessment

Retesting of Liquefaction/Nonliquefaction Case Histories from the 1976 Tangshan Earthquake

A field investigation was carried out to retest liquefaction and nonliquefaction sites from the 1976 Tangshan Earthquake in China. These sites were carefully investigated in 1978/1979 using standard penetration test (SPT) and cone penetration test (CPT) equipment, however the CPT measurements are obsolete because of the now nonstandard cone that was used at the time. In 2007 a modern cone was mobilized to retest 18 select sites that are particularly valuable because; of the intense ground shaking, high fines content, and/or the site did. Of the sites reinvestigated and carefully processed, 13 are considered accurate representative case histories. Two of the sites that were originally documented as exhibiting liquefaction and nonliquefaction have been reassessed as cyclic failure of fine grained soil and removed from consideration for liquefaction triggering. The most important result of these field investigations are 3 nonliquefaction case histories that experienced intense ground shaking. These 3 case histories reside in a region of the liquefaction triggering database that is poorly populated and will help constrain the upper bound of future liquefaction triggering curve