Surficial Displacements Research Articles

Image analysis and LSTM methods for forecasting surficial displacements of a landslide triggered by snowfall and rainfall

AbstractLandslide-prone areas, predominantly located in mountainous regions with abundant rainfall, present unique challenges when subject to significant snowfall at high altitudes. Understanding the role of snow accumulation and melting, alongside rainfall and other environmental variables like temperature and humidity, is crucial for assessing landslide stability. To pursue this aim, the present study focuses first on the quantification of snow accumulated on a slope through a simple parameter obtained with image processing. Then, this parameter is included in a slope displacement prediction analysis carried out with long short-term memory (LSTM) neural network. By employing image processing algorithms and filtering out noise from white-shown rocks, the methodology evaluates the percentage of snow cover in RGB images. Subsequent LSTM forecasts of landslide displacement utilize 28-day historical data on rainfall, snow, and slope movements. The presented procedure is applied to the case of a deep-seated landslide in Italy, a site that in winter 2020–2021 experienced heavy snowfall, leading to significant snow accumulation on the slope. These episodes motivated a study aimed at forecasting the superficial displacements of this landslide, considering the presence of snow both at that time and in the following days, along with humidity and temperature. This approach indirectly incorporates snow accumulation and potential melting phenomena into the model. Although the subsequent winters were characterized by reduced snowfall, including this information in the LSTM model for the period characterized by snow on the slope demonstrated a dependency of the predictions on this parameter, thus suggesting that snow is indeed a significant factor in accelerating landslide movements. In this context, detecting snow and incorporating it into the predictive model emerges as a significant aspect for considering the effects of winter snowfall. The method aims to propose an innovative strategy that can be applied in the future to the study of the landslide analyzed in this paper during upcoming winters characterized by significant snowfall, as well as to other case studies of landslides at high altitudes that lack precise snow precipitation recording instruments.

Fault Surface Rupture Modeling Using Particle Image Velocimetry Analysis of Analog Sandbox Model

This study investigated the correlation between fault kinematics, surficial displacement, and surface rupture geometry patterns between earthquake cycles using particle image velocimetry (PIV) analysis of an analogue sandbox modeling that mimics InSAR observations. The research explored various fault systems, including reverse, normal, and strike-slip faults, through controlled sandbox experiments. The fault surface rupture zone manifests itself due to strain accumulation between two mobile blocks. The displacement magnitude is most pronounced on the surface and is absorbed by the section above the hanging wall or moving block. During fault surface rupture formation, the leading edge of the surface movement consistently extends beyond the anticipated fault surface rupture zone and retreats upon full fault surface rupture development. Subsequently, the distribution of the surface movement is sharply confined by the established fault surface rupture. The key findings of this study underscore the potential of PIV of sandbox modeling for studying fault surface rupture geometry and its development, providing insight into seismic processes. Overall, this work contributes to advancing our knowledge of seismic phenomena and improving strategies for earthquake prediction and mitigation.

Digital terrestrial photogrammetry for a dense monitoring of the surficial displacements of a landslide

A new method for measuring spatially dense surface displacements of a landslide at daily intervals and over a long period of time is here presented. The method allows the evaluation of displacements based on a digital image correlation technique applied to a temporal sequence of photos, daily captured by one or more fixed cameras. In comparison to other topographical method this new procedure has a lower accuracy, but provides distributed daily measurements, spatially very dense over the entire landslide area. The multi-view configuration also allows the reconstruction and the update of the 3D surface of the landslide. This work presents some preliminary results obtained by applying this innovative technique to a complex landslide located in the municipality of Perarolo di Cadore (NE Italy), also known as Sant’Andrea landslide. The landslide is characterized by active slow movements involving detrital deposits, about 30 m thick, overlying gypsum-anhydrite rocks. Its activity is strongly correlated to both heavy and long-lasting rain events and to its particular geological conditions. Recently, the alternating phases characterized by slow movements and significant accelerations led to a progressive enlargement of the affected area. Three cameras installed on a stable slope facing the landslide allow to record the intermittent activity and the peculiar behaviour of different parts of the slope. The displacements thus obtained are also compared with those deriving from conventional techniques. Finally, the accuracy of this new method is discussed.

Method to evaluate the dynamic structure-soil-structure interaction of 3-D buildings arrangement due to seismic excitation

This paper explores the influence of Structure-Soil-Structure Interaction (SSSI) between multiple buildings in a three-dimensional arrangement under seismic excitation. A numerically simplified reduced-order model is proposed to significantly shorten computational run-times for the case of very large clusters of buildings. This formulation has been developed to include the presence of any number of buildings with different heights, widths and interbuilding distances. The auto-rotational spring stiffnesses and inter-rotational spring stiffnesses, of foundations, used in this model are determined by an application of an empirical surficial displacement field (loosely based on a form derived from a Boussinesq elastic half-space approximation that is calibrated against FEA) and inverse system identification using either least-squares or an application of Kronecker products. Different spatial building arrangements are presented, in order to compare with previous research and highlight the versatility of the method. The results showed that the 3D multi-building SSSI can be significantly more complex and difficult to predict than the previous 2D cases in the literature.

A new simple topo-climatic model to predict surface displacement in paraglacial and periglacial mountains of the European Alps: The importance of ground heating index and floristic components as ecological indicators

Landscape evolution is occurring at rapid rates in alpine areas in response to recent climate warming, also due to the susceptibility and the heterogeneity of these environments. Here we present a prediction model of surface displacements that takes into account both topographic and climatic variables. Observed points of surficial displacements have been associated to non-climatic (altitude, slope, solar radiation, till deposit type, deposit age, vegetation coverage) and climatic (days of snow permanence, ground surface temperature index, ground heating index, ground cooling index) variables through a general regression model in the European central Alps.The model output shows the importance of slope and ground heating index (GHI) – an estimation of the amount of energy transferred to the ground, to predict surface displacements independently from the type of considered processes. In particular, the general regression model shows that steep zones with high GHI are more susceptible to undergo periglacial and paraglacial processes producing surface displacements. As expected, slope is fundamental to trigger processes such as gravitation, nivation, solifluction and their interactions. The results of our model emphasize the key role of GHI, highlighting the importance of climate in controlling the surface displacement. Indeed, in areas in which GHI is higher, the ground can remain snow free for a longer time and snow melting can be faster, the former favoring more runoff and slopewash, and the latter promoting the saturation of the deposits consequent to a higher intensity of solifluction and/or mass movements processes.Within the study area, the sites with the largest displacements (>35 cm) were detected where permafrost degradation occurred since 1990. This permafrost degradation process could remain one of the main triggering factors of future surface displacements. Our results confirm that when movement involves material with coarse texture (pebbles and boulders) exceeding the rooting depth, only tolerant plant species can withstand the high movement rates. The areas where this can happen (like rock glaciers or screes) act as a physical barrier to grasslands species not adapted to surface displacements and trying to shift towards higher altitude in response to climate warming. However, plant species not considered as indicators of movement (such as graminoids), can develop also with large surface displacements in specific geomorphic conditions. Therefore, the combination of surface displacement type (deep vs surficial), material texture (fine vs coarse) and vegetation cover (high vs low) and floristic composition can be used as a valuable ecological indicator of movement.Our results suggest that both landscape degradation and vegetation displacement can be rapid especially where the air warming was strong as in the selected study area.

A multi-sensor approach for monitoring a road bridge in the Valencia harbor (SE Spain) by SAR Interferometry (InSAR)

Settlement and angular distortion affecting the construction can cause damages on structures and they could compromise the serviceability of the structure. This work focuses on the monitoring of a bridge located on the south part of the Valencia harbor that shows some opening joints and depressions in the pavement of both transition areas between the abutments and the embankments. For this purpose Advanced Differential Interferometry is used to exploit Synthetic Aperture Radar images (SAR) acquired by ALOS and Cosmo-SkyMed satellite sensors from February 2007 to July 2010 and from May 2010 to August 2012, respectively. This approach permitted to estimate surficial displacements, to identify areas of bridge affected by settlements and angular distortion and to relate them with the observed damages.

Field monitoring of groundwater responses to heavy rainfalls and the early warning of the Kualiangzi landslide in Sichuan Basin, southwestern China

The Kualiangzi landslide was triggered by heavy rainfalls in the “red beds” area of Sichuan Basin in southwestern China. Differing from other bedrock landslides, the movement of the Kualiangzi landslide was controlled by the subvertical cracks and a subhorizontal bedding plane (dip angle < 10°). The ingress of rainwater in the cracks formed a unique groundwater environment in the slope. Field measurement for rainfall, groundwater movement, and slope displacement has been made for the Kualiangzi landslide since 2013. The field monitoring system consists of two rainfall gauges, seven piezometers, five water-level gauges, and two GPS data loggers. The equipments are embedded near a longitudinal section of the landslide, where severe deformation has been observed in the past 3 years. The groundwater responses to four heavy rainfall events were analyzed between June 16 and July 24 in 2013 coincided with the flood season in Sichuan. Results showed that both of the water level and the pore-water pressure increased after each rainfall event with delay in the response time with respect to the precipitation. The maximum time lag reached 35 h occurred in a heavy rainfall event with cumulative precipitation of 127 mm; such lag effect was significantly weakened in the subsequent heavy rainfall events. In each presented rainfall event, longer infiltration period in the bedrock in the upper slope increased the response time of groundwater, compared to that of in the gravels in the lower slope. A translational landslide conceptual model was built for the Kualiangzi landslide, and the time lag was attributed to the gradual formation of the uplift pressure on the slip surface and the softening of soils at the slip surface. Another important observation is the effect on the slope movement which was caused by the water level (H w) in the transverse tension trough developed at the rear edge of the landslide. Significant negative correlation was found for H w and the slope stability factor (F s), in particular for the last two heavy rainfall events, of which the drastic increase of water level caused significant deterioration in the slope stability. The rapid drop (Δ = 22.5 kPa) of pore-water pressure in the deep bedrock within 1 h and the large increase (Δ = 87.3 mm) of surficial displacement were both monitored in the same period. In the end, a four-level early warning system is established through utilizing H w and the displacement rate D r as the warning indicators. When the large deformation occurred in flood season, the habitants at the leading edge of the landslide can be evacuated in time.

Landslide monitoring using multitemporal terrestrial laser scanning for ground displacement analysis

In the analysis of the temporal evolution of landslides and of related hydrogeological hazards, terrestrial laser scanning (TLS) seems to be a very suitable technique for morphological description and displacement analysis. In this note we present some procedures designed to solve specific issues related to monitoring. A particular attention has been devoted to data georeferencing, both during survey campaigns and while performing statistical data analysis. The proper interpolation algorithm for digital elevation model generation has been chosen taking into account the features of the landslide morphology and of the acquired datasets. For a detailed analysis of the different dynamics of the hillslope, we identified some areas with homogeneous behaviour applying in a geographic information system (GIS) environment a sort of rough segmentation to the grid obtained by differentiating two surfaces. This approach has allowed a clear identification of ground deformations, obtaining detailed quantitative information on surficial displacements. These procedures have been applied to a case study on a large landslide of about 10 hectares, located in Italy, which recently has severely damaged the national railway line. Landslide displacements have been monitored with TLS surveying for three years, from February 2010 to June 2012. Here we report the comparison results between the first and the last survey.

Analytical models of volcanic ellipsoidal expansion sources

&lt;p&gt;Modeling non-double-couple earthquakes and surficial deformation in volcanic and geothermal areas usually involves expansion sources. Given an ensemble of ellipsoidal or tensile expansion sources and double-couple ones, it is straightforward to obtain the equivalent single moment tensor under the far-field approximation. On the contrary, the moment tensor interpretation is by no means unique or unambiguous. If the far-field approximation is unsatisfied, the single moment tensor representation is inappropriate. Here we focus on the volume change estimate in the case of single sources, in particular finite pressurized ellipsoidal sources, presenting the expressions for the computation of the volume change and surficial displacement in a closed analytical form. We discuss the implications of different domains of the moment-tensor eigenvalue ratios in terms of volume change computation. We also discuss how the volume change of each source can be obtained from the isotropic component of the total moment tensor, in few cases of coupled sources where the total volume change is null. The new expressions for the computation of the volume change and surficial displacement in case of finite pressurized ellipsoidal sources should make their use easier with respect to the already published formulations.&lt;/p&gt;

Development of a spatial decision support system for monitoring earthquake-induced landslides based on aerial photographs and the finite element method

The evaluation of slope stability is essential for the management of landslide hazards. The integration of spatial information and geomechanical modeling facilitates the understanding and evaluation of landslide hazards. In this study, we use a spatial decision support system (SDSS)—incorporating aerial photographic data, GIS techniques, field investigations, and finite element geomechanical modeling—to analyze the mechanisms of the Hungtaiping landslide, which was induced by the 1999 Chi-Chi earthquake. The analysis clarifies the slide mechanisms that cannot be revealed either by examining aerial photographic or underground exploration data alone. The finite element modeling calibrated using digital aerial photographic data shows that the landslide results from the deformation and slides of the thick colluvium. Surficial displacements in the twenties of meters are attributed to the slide between the colluvium and the bedrock as well as the shear deformation and slides within the colluvium. The landslide SDSS can help determine model parameters, evaluate slide mechanisms and remediation measures, and predict slope behavior for a subsequent earthquake event.

The Paganica Fault and Surface Coseismic Ruptures Caused by the 6 April 2009 Earthquake (L'Aquila, Central Italy)

On 6 April 2009, at 01:32 GMT, an Mw 6.3 seismic event hit the central Apennines, severely damaging the town of L'Aquila and dozens of neighboring villages and resulting in approximately 300 casualties (Istituto Nazionale di Geofisica e Vulcanologia, http://www.ingv.it; MedNet, http://mednet.rm.ingv.it/procedure/events/QRCMT/090406_013322/qrcmt.html). This earthquake was the strongest in central Italy since the devastating 1915 Fucino event ( Mw 7.0). The INGV national seismic network located the hypocenter 5 km southwest of L'Aquila, 8–9 km deep. Based on this information and on the seismotectonic framework of the region, earthquake geologists traveled to the field to identify possible surface faulting (Emergeo Working Group 2009a, 2009b). The most convincing evidence of primary surface rupture is along the Paganica fault, the geometry of which is consistent with seismological, synthetic aperture radar (SAR) and GPS data. Investigation of other known normal faults of the area, i.e. , the Mt. Pettino, Mt. San Franco, and Mt. Stabiata normal faults suggested that these structures were not activated during the April 6 shock (Emergeo Working Group 2009a, 2009b). In this report, we first describe the seismotectonic framework of the area, and then we present the field information that supports the occurrence of surficial displacement on the Paganica fault. The shock of 6 April 2009 occurred in a region that has been struck by past earthquakes (CPTI Working Group 2004; Figure 1) and is in an Apennine sector that contains a complex array of active normal faults ( e.g. , Barchi et al. 2000; Galadini and Galli 2000; Boncio et al. 2004; Roberts and Michetti 2004). In the central Apennines, active faulting and earthquakes result from the ongoing extensional tectonics. The strongest earthquakes in the CPTI04 seismic catalog (CPTI Working Group 2004) occurred on 9 September 1349 ( Mw 6.5) and 2 February …

Deformation of the northern Sumatra accretionary prism from high-resolution seismic reflection profiles and ROV observations

Following the 2004 Great Sumatran–Andaman M w ≈ 9.2 earthquake, high-resolution seismic reflection, multibeam bathymetric and remotely operated vehicle data were acquired to investigate the tectonic framework of the rupture zone and search for evidence of seafloor and near-surface displacement. Three distinct regions off northern Sumatra were investigated; 1) a portion of the Sunda Trench, 2) the adjacent frontal deformation zone, and 3) the seaward flank of the Aceh (forearc) Basin. A thick (> 1.5 km) sediment section within the Sunda Trench shows evidence of shallow normal faulting, possibly representing early stages of assimilation into the accretionary wedge. The frontal deformation zone consists of ridges of predominantly landward-verging thrust folds. Seaward-verging backthrust faults at or near the base of the steep slope commonly reach the seafloor. We do not observe a single, laterally extensive structural offset at the deformation front that might be interpreted as contributing to the 2004 tsunami. Rather, a series of small-offset (tens of metres) faults were noted across this broad zone of the frontal accretionary wedge. The western boundary of the Aceh (forearc) Basin is the West Andaman strike-slip fault, juxtaposing the accretionary complex's forearc high with basin fill sediments. Neither the seismic nor ROV data show evidence of recent seafloor displacement along the fault trace. Basin infill demonstrates consistent along-strike patterns of tilting and seaward subsidence during sedimentation, while modern fill is flat-lying and coherent across the entire basin. Intercalated chaotic layers interpreted as mass transport deposits may record a history of seismicity, but recent examples of such deposits were not observed on the modern seafloor, either seaward of the deformation front or in the Aceh Basin. Lack of any evidence of faulting, offset or disruption of sediments within Aceh Basin suggests that there was little impact of the 2004 earthquake in this area. Distributed faults throughout the frontal deformation zone, combined with observations of landward-verging folds at the deformation front, folding within piggy-back basin sediments, and lack of evidence of disruption along the West Andaman Fault zone and within the forearc basin all support strain partitioning across the margin. A proposed strong wedge interior may act as a backstop during major thrust events, constraining deformation to the frontal deformation zone and the slope apron. Tsunami generation in response to the 2004 event did not result from surficial displacements along a single fault or narrow fault zone at the toe of the deformation front, but was more likely a result of vertical displacement across the entire outer forearc.

Quaternary basin evolution and present tectonic regime in the area of the 1997–1998 Umbria–Marche seismic sequence (central Italy)

Geological and geomorphological surveys have been performed in the area affected by the 1997–1998 Umbria–Marche seismic sequence ( M max=6.0) aimed at defining the Quaternary tectonic history and the characteristics of the present tectonic regime. Data have been collected from: (1) the analysis of the remnant landsurfaces by means of aerial photos and field surveys; (2) geological surveys in the Cesi–San Martino basin and in the easternmost sector of the Colfiorito basin in order to identify deformative features affecting the Quaternary deposits; (3) the analysis of boreholes and geo-electrical data (derived from previous surveys performed in the 1960s) in order to reconstruct the top of the pre-Quaternary substratum in the Colfiorito basin. Two different successions of remnant landsurfaces have been identified along the faults bounding the basins to the east, in the hangingwall and the footwall, respectively. The difference accounts for a fault-controlled evolution of the landscape at least during the Upper Pliocene–Early Pleistocene. The deformation affecting the Quaternary deposits and landforms in the investigated basins indicates a decreasing tectonic activity along the master faults since the Middle Pleistocene. Surface deformation due to tectonics is faint and displayed by gentle warping of the landforms during the late Quaternary. As for the basin geometry, subsurface data show that two minor depressions formed in the Colfiorito Basin during the Quaternary, the oldest one close to the fault bounding the basin, while the youngest (and deepest) formed in the inner portion of the basin. Therefore, the present geometry is different from that of other fault-bounded Quaternary depressions of the central Apennines (typically half-graben basins), showing the maximum depth of the substratum in the area close to the master fault. Tectonic history may be summarised as follows: (1) origin of the Quaternary fault-bounded Colfiorito and Cesi–San Martino basins; (2) evolution of the basins with a half-graben style; (3) significant reduction of tectonic activity since the Middle Pleistocene. During the third phase, the evolution of the basins is no longer related to a half-graben style. In the case of the Colfiorito basin, a new depression is superimposed to on the previous half-graben whose evolution is related to the lowering of the inner portion of the basin through warping. Moreover, present activity does not result in fault-related surficial displacements but only in “continuous” deformation spread over the basins. These conclusions have fundamental implications for the seismotectonic framework of the 1997–1998 earthquake sequence. This deformation style is, indeed, in agreement with the coseismic deformation modelled by means of the SAR interferometry analyses carried out by other institutions during the seismic sequence, and with the lack of evident surface faulting related to the mentioned events in the investigated area. This evidence indicates that the evolution of the investigated area since the Middle Pleistocene resulted from the summation of deformative episodes similar to that which occurred during the recent seismic sequence. As a consequence, no earthquakes with magnitude larger than 6 are expected in the area.

A combined hillslope hydrology/stability model for low-gradient clay slopes in the Italian Dolomites

The temporal trend of displacement of a landslide on a low-gradient clay slope in the Italian Dolomites as a function of precipitation was simulated with a combined hydrological-slope stability model based on groundwater and surficial displacement observations. Piezometric records and lithological profiles from boreholes suggest the occurrence of preferential groundwater flow through a very permeable top layer of about 1 m thickness, which overlies a less permeable, compact clay layer penetrated by dead-end cracks. To simulate groundwater levels in this system, a linear reservoir model with two outlets was applied, where the upper outlet drains the permeable top layer, and the lower outlet drains the dead-end cracks in the clay layer. The reservoir was assigned a bottom boundary level varying in time. This was done to represent an inferred yearly fluctuation of a matric groundwater level due to regional flow, which controls the thickness of the unsaturated part of the clay layer absorbing water from the cracks. Groundwater output from the model was used in a visco-plastic stability model to simulate the velocity of landslide movement, taking into account a phenomenon of strength regain that occurs in the clays along the slip surfaces. Calibration and validation on 3 years of groundwater and displacement data showed that both models yield good results. Thus, good estimates of cumulative landslide displacement were obtained as a function of precipitation. The general concepts underlying the models offer possibilities for regionalization because from a geological point of view, this landslide is typical of many others in the Dolomites.

Measured Movements of Clay Slopes in the Ottawa Area

Natural degradation of slopes is normally considered to involve surficial displacements resulting mainly from frost action, erosion, and downhill creep. Measurements from inclinometer installations in a variety of slope profiles in the Ottawa area show that significant deep-seated movements may occur in these slopes. These movements are associated with seasonal peaks in ground water pressures within the slope and may contribute to the long term degradation of the slope.While the factor of safety against catastrophic failure of a slope is of prime importance, the possible effects of deep-seated slope movements should not be disregarded when considering adjacent land use.

Displacement on the San Andreas fault subsequent to the 1966 Parkfield earthquake

ABSTRACT Immediately following the 1966 Parkfield earthquake a continuing program of fault displacement measurements was undertaken, and several types of instruments were installed in the fault zone to monitor ground motion. In the year subsequent to the earthquake a maximum of at least 20 cm of displacement occurred on a 30 km section of the San Andreas fault, which far exceeded the surficial displacement at the time of the earthquake. The rate of displacement decreased logarithmically during this period in a manner similar to that of the decrease in aftershock activity. After the initial high rate of activity it could be seen that most of the displacement was occurring in 4–6 day epochs of rapid creep following local aftershocks. The variation of fault displacement along the surface trace was measured and shown to be consistent with a vertidal fault surface 44 km long and 14 km deep, along which a shear stress of 2.4 bars was relieved.

Parkfield earthquakes of June 27-29, 1966, Monterey and San Luis Obispo Counties, California—Preliminary report

abstract Two earthquakes, M = 5.3 and 5.5, shook the Parkfield area in southern Monterey County, California, at 0409:56.5 and 0426:13.8 GMT, 28 June 1966. They were preceded by foreshocks on the same day at 0100 and 0115. A third shock, M = 5.0, occurred in the same area at 1953:26.2 on 29 June. The earthquakes were followed by a heavy sequence of aftershocks with epicenters along the San Andreas fault zone extending for about 15 miles southward beyond Cholame in San Luis Obispo County. A P-wave first-motion fault plane solution shows strike of vertical fault plane is N 33°W, coinciding with a surface zone of en echelon fault fractures in the pattern characteristic of right-lateral, strike-slip movement. The motion appears to have an upward component on the west side, at about 20° from pure strike slip. Extensive instrumentation within a few miles of the epicentral district gave unusually complete records from foreshock to aftershock sequence. A strong-motion instrument in the fault zone near Cholame recorded the unusually high horizontal acceleration of 0.5 g. The epicentral region of the earthquakes is on a known active segment of the San Andreas fault. Earthquakes in 1901, 1922, and 1934 in this region were also accompanied by surface faulting. On the published State geologic map, scale 1:250,000, the San Andreas fault zone shows a braided pattern of several branching en echelon major faults. Topographic forms, typical of the features of rift valleys, testify to the recency of fault movements. Small right-lateral surficial displacements had been recognized prior to the late June earthquakes in at least three places on the Parkfield-Cholame trace of the fault. Similar creep, or slippage, has continued since the earthquakes. Extensive nets of survey markers installed by 30 June across the active fault trace had recorded slippage as great as 0.1 inch per day by 12 July. The fault trace associated with the earthquakes is principally in alluvium of unknown depth in Cholame Valley, apparently a faulted graben within the San Andreas fault zone. Under a blanket of Tertiary and Quaternary sedimentary rocks in this part of the southern Coast Ranges, the great fault separates Jurassic-Cretaceous granitic and metamorphic rocks in the western block from Late Jurassic eugeosynclinal sedimentary and volcanic rocks of the Franciscan Formation in the eastern block. In spite of the large horizontal acceleration recorded near the fault, very little building damage occurred in this sparsely populated region. Small concrete and steel bridges in, and adjacent to the fault trace, did not have their structural strength impaired.