Peak Horizontal Acceleration Research Articles

Total Risk Rating and Liquefaction Analysis of Farrokhi Earth Embankment Dam, Eastern Iran

Farrokhi earth embankment dam is located near Qayen in one of the most active seismic regions of Iran (Ferdows seismic state). Due to presence of large active faults in the area, like Dashte-Bayaz and Abiz faults, it is necessary to obtain the total risk rating of the dam and to evaluate the liquefaction potential of the soil layer beneath the dam foundation. The total risk for embankment dam structures depends on two factors, i.e., (i) the seismic hazard rating of the dam site, and, (ii) the risk rating of the dam and appurtenant structures. Bureaue’s method of total risk analysis is used in this paper. Applying this method to Farrokhi dam, the risk factors are determined from different aspects i.e., dam type, age, size, and downstream risk potential. The total risk factor is then determined by considering the effects of each factor as well as seismic vulnerability rating of the dam site. Liquefaction, defined as the transformation of a granular material from a solid to a liquefied state, is a common hazard for civil infrastructures at the time of major earthquakes. In the present study, the procedure recommended by Youd et al. (J Geotech Geoenviron Eng ASCE, 127(10):817–833, 2001), based on SPT results were used. Results of the field geotechnical investigation program carried out on the dam foundation, including SPT data, were used in the liquefaction analysis. Ground motion parameters required in the analysis, i.e. peak horizontal acceleration (amax), were calculated after a careful study of the active faults in the region. Based on the findings of the present study, the alluvial foundation is liquefiable to 3 m of depth in some regions and remedial measures should be taken in advance. An elaborate stability analysis of the dam embankment is deemed necessary.

Effect of lithology and structure on seismic response of steep slope in a shaking table test

Studies on landslides by the 2008 Wenchuan earthquake showed that topography was of great importance in amplifying the seismic shaking, and among other factors, lithology and slope structure controlled the spatial occurrence of slope failures. The present study carried out experiments on four rock slopes with steep angle of 60° by means of a shaking table. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope were analyzed, with much effort on timedomain acceleration responses to horizontal components of seismic shaking. It was found that the amplification factor of peak horizontal acceleration, RPHA, was increasing with elevation of each model slope, though the upper and lower halves of the slope exhibited different increasing patterns. As excitation intensity was increased, the drastic deterioration of the inner structure of each slope caused the sudden increase of RPHA in the upper slope part. In addition, the model simulating the soft rock slope produced the larger RPHA than the model simulating the hard rock slope by a maximum factor of 2.6. The layered model slope also produced the larger RPHA than the homogeneous model slope by a maximum factor of 2.7. The upper half of a slope was influenced more seriously by the effect of lithology, while the lower half was influenced more seriously by the effect of slope structure.

Spatial variation of probabilistic seismic hazard for Mumbai and surrounding region

Mumbai city, the economical capital of India, is located on the west coast of stable intra-plate continental region of Peninsular India which has an experience of significant historical earthquakes in the past. The city stood as the fourth most populous city in the world. Recent seismo-tectonic studies of this city highlighted the presence of active West coast fault and Chiplun fault beneath the Deccan basalt. In the present study, spatial variability of probabilistic seismic hazard for Mumbai region (latitudes of 18.85–19.35°N and longitudes of 72.80–73.15°E at a grid spacing of 0.05°) which includes Mumbai city, Suburban, part of Thane district and Navi Mumbai, in terms of ground motion parameters; peak horizontal acceleration and spectral acceleration at 1.0-s period for 2 and 10 % probability of exceedance in 50 years are generated. The epistemic uncertainty in hazard estimation is accounted by employing seven different ground motion prediction equations developed for worldwide shallow crustal intra-plate environments. Further, the seismic hazard results are deaggregated for Mumbai (latitude 18.94°N, longitude 72.84°E) to understand the relative contributions of earthquake sources in terms of magnitude and distance. The generated hazard maps are compared with the zoning specified by Indian seismic code (IS1893: Part 1 in Indian standard criteria for earthquake-resistant design of structures, Part 1—General provisions and buildings. Bureau of Indian Standards, New Delhi, India, 2002) for rocky site. Present results show an underestimation of potential seismic hazard in the entire study region by non-probabilistic zoning prescribed by IS1893: Part 1 with significantly higher seismic hazard values in the southern part of Navi Mumbai.

Seismic microzonation of a nuclear power plant site with detailed geotechnical, geophysical and site effect studies

This paper highlights the seismic microzonation carried out for a nuclear power plant site. Nuclear power plants are considered to be one of the most important and critical structures designed to withstand all natural disasters. Seismic microzonation is a process of demarcating a region into individual areas having different levels of various seismic hazards. This will help in identifying regions having high seismic hazard which is vital for engineering design and land-use planning. The main objective of this paper is to carry out the seismic microzonation of a nuclear power plant site situated in the east coast of South India, based on the spatial distribution of the hazard index value. The hazard index represents the consolidated effect of all major earthquake hazards and hazard influencing parameters. The present work will provide new directions for assessing the seismic hazards of new power plant sites in the country. Major seismic hazards considered for the evaluation of the hazard index are (1) intensity of ground shaking at bedrock, (2) site amplification, (3) liquefaction potential and (4) the predominant frequency of the earthquake motion at the surface. The intensity of ground shaking in terms of peak horizontal acceleration (PHA) was estimated for the study area using both deterministic and probabilistic approaches with logic tree methodology. The site characterization of the study area has been carried out using the multichannel analysis of surface waves test and available borehole data. One-dimensional ground response analysis was carried out at major locations within the study area for evaluating PHA and spectral accelerations at the ground surface. Based on the standard penetration test data, deterministic as well as probabilistic liquefaction hazard analysis has been carried out for the entire study area. Finally, all the major earthquake hazards estimated above, and other significant parameters representing local geology were integrated using the analytic hierarchy process and hazard index map for the study area was prepared. Maps showing the spatial variation of seismic hazards (intensity of ground shaking, liquefaction potential and predominant frequency) and hazard index are presented in this work.

SEISMIC HAZARD ANALYSIS FOR MYANMAR

In this study, the seismic hazards of Myanmar are analyzed based on both deterministic and probabilistic scenarios. The area of the Sumatra–Andaman Subduction Zone is newly defined and the lines of faults proposed previously are grouped into nine earthquake sources that might affect the Myanmar region. The earthquake parameters required for the seismic hazard analysis (SHA) were determined from seismicity data including paleoseismological information. Using previously determined suitable attenuation models, SHA maps were developed. For the deterministic SHA, the earthquake hazard in Myanmar varies between 0.1 g in the Eastern part up to 0.45 g along the Western part (Arakan Yoma Thrust Range). Moreover, probabilistic SHA revealed that for a 2% probability of exceedance in 50 and 100 years, the levels of ground shaking along the remote area of the Arakan Yoma Thrust Range are 0.35 and 0.45 g, respectively. Meanwhile, the main cities of Myanmar located nearby the Sagaing Fault Zone, such as Mandalay, Yangon, and Naypyidaw, may be subjected to peak horizontal ground acceleration levels of around 0.25 g.

Response of High-Strength Rock Slope to Seismic Waves in a Shaking Table Test

Studies on landslides by the 2008 Wenchuan earthquake showed that the topography is of great importance in amplifying the seismic shaking. The present study carried out experiments on rock slopes by means of a shaking table. The recorded Wenchuan earthquake waves are scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope simulating high‐strength rocks are analyzed, with much effort on acceleration responses to both horizontal and vertical components of seismic shaking. It is found that the amplification factor of peak horizontal acceleration (PHA) is increasing with elevation of the model slope, though the upper and lower halves of the slope exhibit different increasing patterns. The amplification factor of peak vertical acceleration (PVA) exhibits a lying S‐shaped changing trend with the elevation, indicating attenuations of PVAs at the toe and top of a slope. In addition, the XZ ‐direction shaking produces a horizontal and vertical response stronger than X ‐direction and Z ‐direction shaking alone. Both PHA and PVA increase with the excitation intensity. However, the corresponding amplification factors generally decrease, indicating the acceleration response of a slope weakens with the excitation intensity of shaking. Finally the statistic of ratio of PVA to PHA indicates that 85% of the slope height, especially the upper middle part, is likely subject to PVAs greater than or equal to 2/3 of PHA and 32% of the slope height to PVAs greater than or equal to PHA. This indicates the nonignorable role of PVA in responses of a slope to an earthquake and necessity of considering during design work.

Assessment of Seismically Induced Landslide Hazard for the State of Karnataka Using GIS Technique

Landslide hazards are a major natural disaster that affects most of the hilly regions around the world. In India, significant damages due to earthquake induced landslides have been reported in the Himalayan region and also in the Western Ghat region. Thus there is a requirement of a quantitative macro-level landslide hazard assessment within the Indian subcontinent in order to identify the regions with high hazard. In the present study, the seismic landslide hazard for the entire state of Karnataka, India was assessed using topographic slope map, derived from the Digital Elevation Model (DEM) data. The available ASTER DEM data, resampled to 50 m resolution, was used for deriving the slope map of the entire state. Considering linear source model, deterministic seismic hazard analysis was carried out to estimate peak horizontal acceleration (PHA) at bedrock, for each of the grid points having terrain angle 10A degrees and above. The surface level PHA was estimated using nonlinear site amplification technique, considering B-type NEHRP site class. Based on the surface level PHA and slope angle, the seismic landslide hazard for each grid point was estimated in terms of the static factor of safety required to resist landslide, using Newmark's analysis. The analysis was carried out at the district level and the landslide hazard map for all the districts in the Karnataka state was developed first. These were then merged together to obtain a quantitative seismic landslide hazard map of the entire state of Karnataka. Spatial variations in the landslide hazard for all districts as well as for the entire state Karnataka is presented in this paper. The present study shows that the Western Ghat region of the Karnataka state is found to have high landslide hazard where the static factor of safety required to resist landslide is very high.

Site specific prediction equations for peak acceleration of ground motion due to earthquakes induced by underground mining in Legnica-Głogów Copper District in Poland

Ground motion database from the region of Żelazny Most tailings pond, the largest in Europe ore-flotation waste repository, is used to identify ground motion prediction equations (GMPE-s) for peak horizontal and peak vertical acceleration. A GMPE model including both geometrical spreading and anelastic damping terms cannot be correctly identified and the model with only spreading term is accepted. The analysis of variance of this model’s residuals with station location as grouping variable indicates that station locations contribute significantly to the observed ground motion variability. Therefore, a site specific GMPE model with relative site amplifications is assessed. Despite short distances among stations, the amplification considerably vary from point to point, up to 1.8 times for the horizontal and 3.5 times for the vertical peak amplitude. The model including site effects enhances GMPE-s fit to observations, explains more than 60% dependent variables variability and correctly accounts for site effects.

Delineation of seismic source zones based on seismicity parameters and probabilistic evaluation of seismic hazard using logic tree approach

The delineation of seismic source zones plays an important role in the evaluation of seismic hazard. In most of the studies the seismic source delineation is done based on geological features. In the present study, an attempt has been made to delineate seismic source zones in the study area (south India) based on the seismicity parameters. Seismicity parameters and the maximum probable earthquake for these source zones were evaluated and were used in the hazard evaluation. The probabilistic evaluation of seismic hazard for south India was carried out using a logic tree approach. Two different types of seismic sources, linear and areal, were considered in the present study to model the seismic sources in the region more precisely. In order to properly account for the attenuation characteristics of the region, three different attenuation relations were used with different weightage factors. Seismic hazard evaluation was done for the probability of exceedance (PE) of 10% and 2% in 50 years. The spatial variation of rock level peak horizontal acceleration (PHA) and spectral acceleration (Sa) values corresponding to return periods of 475 and 2500 years for the entire study area are presented in this work. The peak ground acceleration (PGA) values at ground surface level were estimated based on different NEHRP site classes by considering local site effects.

Seismic hazard across Bulgaria and neighbouring areas: extreme magnitude recurrence and strong ground shaking

A contemporary probabilistic seismic hazard assessment (PSHA) study for Bulgaria and the surrounding Balkan area is performed under constraints of a newly developed, fit-for-purpose historical earthquake catalogue and the theory of extreme values. Sensitivity analyses are first adopted as preparatory reviews on subsets of the adopted data to determine suitable values for the constraints of cut-off magnitude threshold, sample extreme interval and start year of catalogue data to impose on the parent database for both the full region considered as well as significant urban centres within it. Maximum estimates are then determined for magnitude recurrence hazard using Gumbel’s third asymptotic extreme values distribution for return periods of 50 and 100 years, and also these time intervals at 90 % probability of not being exceeded (PNBE). Gumbel’s first asymptotic extreme values distribution is also used with carefully selected, geographically relevant ground motion models for peak horizontal ground acceleration, PGA(h), and peak horizontal ground velocity, PGV(h), for the same return periods. The former provides direct comparison with the current EUROCODE 8 anti-seismic building code standard promoted across Europe, the previous GSHAP and SESAME hazard mapping projects as well as a number of recent studies. Sofia is forecast an upper bound magnitude of 7.33 M w (±0.78) compared with 7.31 M w (±0.55) for the full Balkan extent and 7.24 M w (±0.70) for the political triple junction area of southwest Bulgaria, viz., Bulgaria, Greece and The Former Yugoslav Republic of Macedonia. Sofia is also forecast a 475-year return period (equivalent to a 50-year return period at 90 % PNBE) magnitude of 7.27 M w, with an equivalent PGA (the standard EUROCODE 8 metric) of 156 cm s−2 and PGV of 13 cm s−1.

Probabilistic seismic hazard analysis of Tripura and Mizoram states

A probabilistic seismic hazard analysis for the states of Tripura and Mizoram in North East India is presented in this paper to evaluate the ground motion at bedrock level. Analyses were performed considering the available earthquake catalogs collected from different sources since 1731-2010 within a distance of 500 km from the political boundaries of the states. Earthquake data were declustered to remove the foreshocks and aftershocks in time and space window and then statistical analysis was carried out for data completeness. Based on seismicity, tectonic features and fault rupture mechanism, this region was divided into six major seismogenic zones and subsequently seismicity parameters (a and b) were calculated using Gutenberg-Richter (G-R) relationship. Faults data were extracted from SEISAT (Seismotectonic atlas of India, Geological Survey of India, New Delhi, 2000) published by Geological Survey of India and also from satellite images. The study area was divided into small grids of size 0.05A degrees A xA 0.05A degrees (approximately 5 km x 5 km), and the hazard parameters (rock level peak horizontal acceleration and spectral accelerations) were calculated at the center of each of these grid cells considering all the seismic sources within a radius of 500 km. Probabilistic seismic hazard analyses were carried out for Tripura and Mizoram states using the predictive ground motion equations given by Atkinson and Boore (Bull Seismol Soc Am 93:1703-1729, 2003) and Gupta (Soil Dyn Earthq Eng 30:368-377, 2010) for subduction belt. Attenuation relations were validated with the observed PGA values. Results are presented in the form of hazard curve, peak ground acceleration (PGA) and uniform hazard spectra for Agartala and Aizawl city (respective capital cities of Tripura and Mizoram states). Spatial variation of PGA at bedrock level with 2 and 10 % probability of exceedance in 50 years has been presented in the paper.

CPT-based Seismic Liquefaction Potential Evaluation Using Multi-gene Genetic Programming Approach

This study examines the potential of multi-gene genetic programming (MGGP) based classification approach to evaluate liquefaction potential of soil in terms liquefaction index (LI) using a large database from post liquefaction cone penetration test (CPT) measurements and field manifestations. The database consists of CPT measurements; cone tip resistance (qc), friction ratio (Rf), vertical total stress (σv) and vertical effective stress of soil (σv′), seismic parameters; peak horizontal ground surface acceleration (amax) and earthquake moment magnitude (Mw), and the depth under consideration (z). The MGGP models (Model-I and Model-II) are developed for predicting occurrence and non-occurrence of liquefaction on basis of combination of above input parameters. The performance of the Model-I (95 %) is found to be more efficient compared to available artificial neural network model (91 %) and that of the Model-II (97 %) is found to be at par with the available support vector machine model (97 %) in terms of rate of successful prediction of liquefied and non-liquefied cases for testing data. Using an independent database of 96 cases, the overall classification accuracies are found to be 87 and 86 % for Model-I and Model-II respectively. Sensitivity analyses are made to identify the important parameters contributing to the prediction of LI.

Modelling of probability liquefaction based on standard penetration tests using the jointly distributed random variables method

Soil liquefaction during an earthquake can be a major cause of damage to structures. The inherent variability of the soil parameters which affect liquefaction potential dictates that the problem is of a probabilistic nature rather than being deterministic. Probabilistic assessment of liquefaction potential has received considerable attention in the past few years. In this research, the Jointly Distributed Random Variables (JDRV) method is used as an analytical method to develop a model for probability of liquefaction potential based on standard penetration tests. The selected stochastic parameters are corrected SPT blow count and stress reduction factor, which are modeled using a truncated normal probability density function and the peak horizontal earthquake acceleration ratio and earthquake magnitude, which are considered to have a truncated exponential probability density function. The depth of water table and fines content are regarded as constant parameters. The results of JDRV method are verified with those of the Monte Carlo simulation. It is shown that the moment magnitude is the most effective parameter in soil liquefaction potential. Comparison of the model results indicates reasonable performance of the proposed approach in assessment of probability of liquefaction and empirical data.

Damage to Steel Buildings Observed after the 2011 Tohoku-Oki Earthquake

A joint U.S.–Japan reconnaissance team examined the damage to steel building structures caused by the 2011 Tohoku-oki earthquake. In the city of Sendai, where the peak horizontal ground acceleration exceeded 1 g, the majority of steel buildings performed well. Buildings that used older cladding systems for external finish sustained damage to their claddings even if their structural performance was excellent. Damage to a few braced frames offer insight into the seismic design of bracing connections. In areas attacked by the violent tsunami, many steel buildings stood upright after the tsunami subsided, although these buildings lost much of their external and internal finishes along with their contents. These steel buildings did not provide safe shelter for tsunami evacuation when the building submerged under the tsunami wave. A number of buildings suffered foundation failure, which was likely caused by scouring or liquefaction or a combination of multiple effects.

Vertical acceleration response of horizontally excited reinforced walls

ABSTRACT: An understanding of the vertical acceleration response of geosynthetic-reinforced slopes subjected to horizontal input ground excitations is essential to robust seismic design. A series of stepwise intensified shaking tests was performed using simple sinusoidal waves with various horizontal peak ground accelerations (HPGA = 0.2–1.0g where g = gravitational acceleration) and wave frequencies (f = 3, 6 and 15 Hz) to investigate vertical acceleration responses at the crest of a reinforced model slope subjected to horizontal input ground excitations. Vertical accelerations at the edge of the slope crest (av1) occurred under relatively small HPGA associated with a negligibly small displacement of the slope. A large vertical acceleration of the unreinforced zone (av2) occurred under relatively large HPGA associated with a large displacement of the slope. Measured horizontal peak acceleration (ahp) against vertical peak acceleration (avp) at the crest of the slope indicate that values of avp under a specific HPGA increase with increasing input wave frequency. At the verge of the ultimate displacement state, values of avp at the crest of the unreinforced zone were consistently greater than those for the crest of the reinforced zone, suggesting that a downward slump of the failure wedge behind the reinforced zone occurred at the ultimate displacement state of the slope. Pseudo-static stability analyses were performed for the tested slopes based on the observed range of vertical-to-horizontal acceleration ratio (λ) at the crest of slopes loaded with f = 3 and 6 Hz. It was shown that the influence of λ on the critical seismic coefficient (khc) of the slope increases with increasing reinforcement force. Values of khc decreased by 8–30% when λ increased from 0 to +1.5, indicating that a vertical acceleration induced by the slump of the soil mass plays a role in destabilising the slope and/or in increasing the plastic displacement of the slope.

Empirical ground-motion relations using moderate earthquakes recorded by Medellín–Aburrá Valley (Colombia) strong-motion networks

We tested attenuation relations obtained for different regions of the world to verify their suitability to predict strong-motion data recorded by Medellin and Aburra Valley Accelerographic Networks. We used as comparison criteria, the average of the difference between the observed and the predicted data as a function of epicenter distance and its standard deviation. We also used the approach developed by Sherbaum et al. (Bull Seism Soc Am 94:2164–2185, 2004) that provides a method to evaluate the overall goodness-of-fit of ground-motion prediction equations. The predictive models selected use a generic focal depth. We found that this parameter has an important influence in the ground-motion predictions and must be taken into account as an independent variable. We also found important to characterize the local soil amplification to improve the attenuation relations. We found empirical relations for peak horizontal acceleration PGA and velocity PGV based on the Kamiyama and Yanagisawa (Soils Found 26:16–32, 1986) approach. $$\begin{aligned} \log _{10} (PGA)=0.5886M_L -1.0902\log _{10}(R)-0.0035H+C_{st}\pm 0.\text{29} \end{aligned}$$ $$\begin{aligned} \log _{10} (PGV)=0.7255M_L -1.8812\log _{10}(R)-0.0016H+C_{st}\pm 0.36 \end{aligned}$$ where PGA is measured in cm/s\(^{2}\) and PGV in cm/s, \(M_{L}\) is local magnitude in the range 2.8–6.5, \(R\) is epicentral distance up to 290 km, \(H\) is focal depth in km and \(C_{st}\) is a coefficient that accounts for the site response due to soil conditions of each recording station. The introduction of focal depth and local site conditions as independent variables, minimize the residuals and the dispersion of the predicted data. We conclude that \(H\) and \(C_{st}\) are sensitive parameters, having a strong influence on the strong-motion predictions. Using the same functional form, we also propose an empirical relation for the root mean square acceleration a\(_\mathrm{rms}\): $$\begin{aligned} \log _{10} \left( {a_{rms} } \right)=0.4797M_L -1.1665\log _{10} (R)-0.00201H+C_{st}\pm 0.40 \end{aligned}$$ where a\(_\mathrm{rms}\) is measured in cm/s\(^{2}\), from the S-wave arrival and using a window length equal to the rupture duration. The other variables are the same as those for PGA and PGV. The site correction coefficients \(C_{st}\) found for PGA, PGV and a\(_\mathrm{rms}\) show a similar trend indicating a good correlation with the soil conditions of the recording sites.

Geomechanical Modeling of Fault Responses and the Potential for Notable Seismic Events During Underground CO2 Injection

We summarize a number of recent modeling studies related to the potential for fault reactivations and induced seismicity during underground CO2 injection. The model simulations were conducted using coupled multiphase fluid flow and geomechanics, including fault-frictional weakening enabling analysis of sudden (seismic) fault rupture, with some of the numerical analyses extended to dynamic modeling of seismic source, wave propagation, and ground motion. These model simulations show that the critical factors in determining the likelihood and magnitude of such an event are the local in situ stress field, fault orientation and size, fault strength, and injection pressure. We analyzed the case of activation of a 1km long minor fault that might have gone undetected during the site investigation and show that the maximum seismic magnitudes would likely be less than about 3.6, even if the entire 1km fault would to be activated. We then include seismic wave propagation generated by the rupture and show how the acceleration and deceleration of the rupture generate waves and result in a peak ground acceleration of about 0.1g, except for a localized –0.6g of horizontal peak acceleration at the faults intersection with the ground surface. The modeling shows that these are high frequency events that would not cause any substantial damage but could certainly be felt by the local population. We may also considered that fault reactivation, even associated with relatively small seismic or aseismic events, could potentially increase CO2 seepage out of the intended storage complex and therefore reduce the effectiveness of a CO2 storage operation. Under these circumstances, we recommend a staged, learn-as-you-go approach, involving a gradual increase of injection rates combined with continuous monitoring of geomechanical changes, as well as siting beneath a multiple layered overburden for multiple flow barrier protection, should an unexpected deep fault activation occur.

Amateur football pitches: Mechanical properties of the natural ground and of different artificial turf infills and their biomechanical implications

Artificial turf is being used more and more often. It is more available than natural turf for use, requires much less maintenance and new products are able to comply with sport performance and athletes’ safety. The purpose of this paper is to compare the mechanical and biomechanical responses of two different artificial turf infills (styrene butadiene rubber, from granulated vehicle tires, and thermoplastic rubber granules) and to compare them to the performance of natural fields where amateurs play (beaten earth, substantially). Three mechanical parameters have been calculated from laboratory tests: energy storage, energy losses and surface traction coefficient; results have been correlated with peak accelerations recorded on an instrumented athlete, on the field. The natural ground proved to be stiffer (−15% penetration depth for a given load), and to have a lower dynamic traction coefficient (−48%); the different kinds of infill showed significantly different stiffnesses (varying by more than 23%) and damping behaviour (varying by more than 31%). In running, peak vertical accelerations were lowest in the artificial ground with thermoplastic rubber granules, while, in slalom, both artificial grounds produced higher horizontal peak accelerations compared to the natural ground. Results are discussed in terms of their implications for athletic performance and injury risk.

Observations of seismic activity in Southern Lebanon

Recent seismic activity in southern Lebanon is of particular interest since the tectonic framework of this region is poorly understood. In addition, seismicity in this region is very infrequent compared with the Roum fault to the east, which is seismically active. Between early 2008 and the end of 2010, intense seismic activity occurred in the area. This was manifested by several swarm-like sequences and continuous trickling seismicity over many days, amounting in total to more than 900 earthquakes in the magnitude range of 0.5 ≤ M d ≤ 5.2. The region of activity extended in a 40-km long zone mainly in a N-S direction and was located about 10 km west of the Roum fault. The largest earthquake, with a duration magnitude of M d = 5.2, occurred on February 15, 2008, and was located at 33.327° N, 35.406° E at a depth of 3 km. The mean-horizontal peak ground acceleration observed at two nearby accelerometers exceeded 0.05 g, where the strongest peak horizontal acceleration was 55 cm/s2 at about 20 km SE of the epicenter. Application of the HypoDD algorithm yielded a pronounced N-S zone, parallel to the Roum fault, which was not known to be seismically active. Focal mechanism, based on full waveform inversion and the directivity effect of the strongest earthquake, suggests left-lateral strike-slip NNW-SSE faulting that crosses the NE-SW traverse faults in southern Lebanon.

Potential collapse of the upper slope and tsunami generation on the Great Barrier Reef margin, north-eastern Australia

Analysis of high-resolution multibeam bathymetry and seismic profiles in the Noggin Passage region, north-eastern Australia, has identified a small area (Noggin block) in the upper-slope offshore Cairns that may potentially collapse and generate a tsunami wave. The Noggin block extends from 340 to 470 m depth covering a roughly circular (2.4 km long and 3.7 km wide) area of about 5.3 km2. The well-defined margins of the block correspond to different bounding seabed features. These features include steep headscarps, small landslides and a group of aligned circular pockforms up to 500 m wide and 20 m deep. Slope stability simulations indicate that the Noggin block is stable under normal present-day gravitational conditions on the upper slope. However, block failure may result under external loads, such as those produced by earthquakes. Failure modelling shows that critical peak horizontal accelerations of 0.2–0.4 g could lead to the collapse of the Noggin block. In north-eastern Australia, these acceleration values would involve earthquakes generated at short hypocentral distances and short periods. The collapse of the potential sediment slide mass of about 0.86 km3 (162 m average thickness) may lead to the formation of a landslide-generated tsunami wave. Semi-empirical equations indicate the collapse of this mass would yield a 7–11-m high three-dimensional tsunami wave. These waves could reach an estimated run-up height at the coast of 5–7 m. Our first-order approach highlights the potential consequences for nearby coastal communities, the need for better sediment characterisation in the study area, and the systematic identification of other areas prone to slope failures along the Great Barrier Reef margin.