CALIBRATION OF 1-D NUMERICAL CODES SOFTWARE FOR SITE RESPONSE ANALYSES

Ground response analyses are used to predict surface ground motions for development of design response spectra, to evaluate dynamic stresses and strains for evaluation of earthquake hazards, and to determine the earthquake induced forces that can lead to instability of earth-retaining structures. The effects of local soil on ground motion are commonly evaluated by performing numerical analyses either in frequency or time domains.In order to evaluate the differences between frequency and time domain analysis, several analyses were conducted for homogenous stiff soil deposit with respective codes which are SHAKE and D-MOD2000. Linear and non linear analyses have been conducted. The non linear analyses with D-MOD2000 code have been carried out by using different frequencies in the Rayleigh damping formulation, i.e. fundamental and predominant frequency. For linear, PGA 0.1g is used in the analysis while for non linear PGA is scaled into three different value of 0.1, 0.3, and 0.5g.The results for both linear and non linear approach are similar. For the non linear analyses, it is shown that the curves derived using predominant frequency perform better than those using fundamental frequency. Main differences are for non linear approach where the differences between two codes are higher for higher input motion. As the calibration using predominant frequency between the two codes perform good, the respective codes are applied to evaluate soil response in Sant’ Agostino and San Carlo, in terms of PGA, due to May 20th 2012 Emilia Earthquake. There are 139 accelerometric station recorded strong motion. In this analysis, we consider one record which is in Mirandola station, the closest recording station where the Magnitude in epicentral area was 5.9 and 5.8 in Mirandola station. The recorded surface motion in Mirandola is transferred to the bedrock in 112 m depth and used as input motion for the two evaluated sites, San Carlo village and nearby municipality Sant’Agostino on 17 km distance from Mirandola station. The preliminary data presented here shows the PGA recorded in the bedrock of Mirandola station is 0.75g, while in Sant’Agostino and San Carlo is 0.92g and 0.81g

CALIBRATION OF 1-D NUMERICAL CODES SOFTWARE FOR SITE RESPONSE ANALYSES

Ground response analyses are used to predict surface ground motions for development of design response spectra, to evaluate dynamic stresses and strains for evaluation of earthquake hazards, and to determine the earthquake induced forces that can lead to instability of earth-retaining structures. The effects of local soil on ground motion are commonly evaluated by performing numerical analyses either in frequency or time domains.In order to evaluate the differences between frequency and time domain analysis, several analyses were conducted for homogenous stiff soil deposit with respective codes which are SHAKE and D-MOD2000. Linear and non linear analyses have been conducted. The non linear analyses with D-MOD2000 code have been carried out by using different frequencies in the Rayleigh damping formulation, i.e. fundamental and predominant frequency. For linear, PGA 0.1g is used in the analysis while for non linear PGA is scaled into three different value of 0.1, 0.3, and 0.5g.The results for both linear and non linear approach are similar. For the non linear analyses, it is shown that the curves derived using predominant frequency perform better than those using fundamental frequency. Main differences are for non linear approach where the differences between two codes are higher for higher input motion. As the calibration using predominant frequency between the two codes perform good, the respective codes are applied to evaluate soil response in Sant' Agostino and San Carlo, in terms of PGA, due to May 20th 2012 Emilia Earthquake. There are 139 accelerometric station recorded strong motion. In this analysis, we consider one record which is in Mirandola station, the closest recording station where the Magnitude in epicentral area was 5.9 and 5.8 in Mirandola station. The recorded surface motion in Mirandola is transferred to the bedrock in 112 m depth and used as input motion for the two evaluated sites, San Carlo village and nearby municipality Sant'Agostino on 17 km distance from Mirandola station. The preliminary data presented here shows the PGA recorded in the bedrock of Mirandola station is 0.75g, while in Sant'Agostino and San Carlo is 0.92g and 0.81g

Earthquake Geotechnical Engineering Aspects of the 2012 Emilia-Romagna Earthquake (Italy)

On May 20, 2012 an earthquake of magnitude ML=5.9 struck the Emilia Romagna Region of Italy and a little portion of Lombardia Region. Successive earthquakes occurred on May 29, 2012 with ML=5.8 and ML=5.3. The earthquakes caused 27 deaths, of which 13 on industrial buildings. The damage was considerable. 12,000 buildings were severely damaged; big damages occurred also to monuments and cultural heritage of Italy, causing the collapse of 147 campaniles. The damage is estimated in about 5-6 billions of euro. To the damage caused to people and buildings, must be summed the indirect damage due to loss of industrial production and to the impossibility to operate for several months. The indirect damage could be bigger than the direct damage caused by the earthquake. The resilience of the damaged cities to the damage to the industrial buildings and the lifelines was good enough, because some industries built a smart campus to start again to operate in less of one month and structural and geotechnical guidelines were edited to start with the recovering the damage industrial buildings. In the paper a damage survey is presented and linked with the ground effects. Among these, soil amplification and liquefaction phenomena are analyzed, basing on the soil properties evaluation by field and laboratory tests. Particular emphasis is devoted to the damaged suffered by the industrial buildings and to the aspects of the remedial work linked with the shallow foundation inadequacy and to the liquefaction mitigation effects

Geology, structure and metamorphism of the Mai khola area, southwestern part of Ilam Bazaar, eastern Nepal

The study area consists of three tectonic zones from south to north, they are the Siwalik, Lesser Himalayan Sequence and Higher Himalaya Crystalline thrust sheet. The Lesser Himalayan Sequence is composed of chlorite, biotite and garnet grade metasediments and augen gneiss. The Higher Himalayan Crystalline thrust sheet is composed of kyanite to sillimanite grade paragneiss, orthogneiss and quartzite. The area is affected mainly by two deformational episodes (i) Syn-MCT metamorphic ductile deformation and (ii) Post-MCT metamorphic deformation. Syn-MCT metamorphic ductile deformation is characterized by (a) development of bedding-parallel foliation and syn-metamorphic stretching lineations trending NNE- SSW and (b) development of S-C structure. Three sub phases of the post-MCT metamorphic deformation are observed in the study area viz. (a) development of folds, (b) new generation of foliation and extensional shearing features and (c) small-scale brittle fault, shear bands and cross-cut veins. The Lesser Himalayan Sequence has been metamorphosed to greenschist-amphibolite facies whereas the Higher Himalayan Crystalline thrust sheet has been metamorphosed to amphibolite to granulite facies. At least two metamorphic events could be recorded in the Lesser Himalayan Sequence. During Pre Himalayan metamorphic phase, the Lesser Himalayan Sequence might be metamorphosed up to anchizone grade prograde metamorphism(?). But Eo-Himalayan metamorphic phase could not affect the Lesser Himalayan Sequence. The Neo-Himalayan (Syn-MCT) metamorphic phase has been recorded on S-C fabric and is revealed by inverted metamorphic zonation in the Lesser Himalayan Sequence. The final phase in the Lesser Himalayan Sequence was retrograde phase shown by chloritization of garnet and biotite. At least three metamorphic events are recognized in the Higher Himalayan Crystalline thrust sheet of the study area. In the Eo-Himalayan (pre-MCT) metamorphic event kyanite grade prograde metamorphism has been occurred. This is followed by sillimanite grade retrograde metamorphism (lower P/high T) on the hanging wall of MCT and is assigned as Neo-Himalayan (Syn-MCT) metamorphic event. Finally the replacement of garnet and biotite by chlorite is the third (retrogressive metamorphic event) occurred during post MCT movement

Quantifying surface process dynamics during extreme events from storm characteristics and landslide inventories

International audienceExtreme precipitation events drive landsliding in many regions across the globe and are an important part of the erosional cycle and related hazards. The intensity and frequency of extreme events are likely increasing due to rising global temperatures, causing greater future threat to society and an urgent need to quantify the relationships between surface process dynamics and extreme events. In steep mountain belts, orography also plays a role in focusing precipitation and intensifying erosion. Yet, the influence of orography on the intensity-duration characteristics of extreme precipitation remains a subject of debate because we lack spatially distributed and high time-resolution gauge datasets needed to resolve convective-scale, short-duration storm events and satellite-derived precipitation products struggle to accurately resolve precipitation gradients over areas of high relief and altitude. Annual periods of monsoon-related landsliding in the Himalaya offer a natural laboratory in which to explore relationships between extreme precipitation, orography and landsliding processes. Here we scale the NASA’s Global Precipitation Measurement (GPM) IMERG 30-minute, 0.1x0.1 degree product with local rain gauge data to produce high-temporal resolution records used to characterize extreme rainfall events (EREs) in central Nepal where hundreds of shallow landslides occur each summer. Individual storms from the time series are defined using the average inter-accumulation time as a measure for the minimum dry period between storms and extreme storms are extracted from the series using a 90th percentile threshold for each gauge station. Variability in storm characteristics is defined using paired K-means agglomerative cluster and principal component analyses to evaluate spatial patterns in storm characteristics over a 10 year period compared to annual landslide inventories. Spatial patterns emerge that suggest orography increases the intensity and frequency of storms, which in turn focuses landsliding in specific, and potentially predictable, regions along the steep windward flank of the mountain belt

Large paleoearthquake timing and displacement near Damak in eastern Nepal on the Himalayan Frontal Thrust

An excavation across the Himalayan Frontal Thrust near Damak in eastern Nepal shows displacement on a fault plane dipping similar to 22 degrees has produced vertical separation across a scarp equal to 5.5m. Stratigraphic, structural, geometrical, and radiocarbon observations are interpreted to indicate that the displacement is the result of a single earthquake of 11.33.5m of dip-slip displacement that occurred 1146-1256A.D. Empirical scaling laws indicate that thrust earthquakes characterized by average displacements of this size may produce rupture lengths of 450 to >800km and moment magnitudes M-w of 8.6 to >9. Sufficient strain has accumulated along this portion of the Himalayan arc during the roughly 800years since the 1146-1256A.D. earthquake to produce another earthquake displacement of similar size. Plain Language Summary The densely populated country of Nepal sits above the Himalayan Frontal Thrust fault. It is repeated displacements on this fault that are responsible for the uplift of the Himalaya mountains and considered capable of producing great earthquakes. Here we excavate a trench across the fault to show a great earthquake occurred 1146 -1256 AD in eastern Nepal. It has been a sufficiently long time since then that stresses have accumulated to a level capable of producing another such great earthquake

The size, distribution, and mobility of landslides caused by the 2015 Mw7.8 Gorkha earthquake, Nepal

Coseismic landslides pose immediate and prolonged hazards to mountainous communities, and provide a rare opportunity to study the effect of large earthquakes on erosion and sediment budgets. By mapping landslides using high-resolution satellite imagery, we find that the 25 April 2015 Mw7.8 Gorkha earthquake and aftershock sequence produced at least 25,000 landslides throughout the steep Himalayan Mountains in central Nepal. Despite early reports claiming lower than expected landslide activity, our results show that the total number, area, and volume of landslides associated with the Gorkha event are consistent with expectations, when compared to prior landslide-triggering earthquakes around the world. The extent of landsliding mimics the extent of fault rupture along the east-west trace of the Main Himalayan Thrust and increases eastward following the progression of rupture. In this event, maximum modeled Peak Ground Acceleration (PGA) and the steepest topographic slopes of the High Himalaya are not spatially coincident, so it is not surprising that landslide density correlates neither with PGA nor steepest slopes on their own. Instead, we find that the highest landslide density is located at the confluence of steep slopes, high mean annual precipitation, and proximity to the deepest part of the fault rupture from which 0.5–2 Hz seismic energy originated. We suggest that landslide density was determined by a combination of earthquake source characteristics, slope distributions, and the influence of precipitation on rock strength via weathering and changes in vegetation cover. Determining the relative contribution of each factor will require further modeling and better constrained seismic parameters, both of which are likely to be developed in the coming few years as post-event studies evolve. Landslide mobility, in terms of the ratio of runout distance to fall height, is comparable to small volume landslides in other settings, and landslide volume-runout scaling is consistent with compilations of data on larger slope failures. In general, the size ratios of landslide source area to full landslide area are smaller than global averages, and hillslope length seems to largely control runout distance, which we propose reflects a topographic control on landslide mobility in this setting. We find that landslide size dictates runout distance and that more than half of the landslide debris was deposited in direct connection with stream channels. Connectivity, which is defined as the spatial proximity of landslides to fluvial channels, is greatest for larger landslides in the high-relief part of the High Himalaya. Although these failures are less abundant than those at lower elevations, they may have a disproportionate impact on sediment dynamics and cascading hazards, such as landslide reactivation by monsoon rainfall and landslide dams that lead to outburst floods. The overall high fluvial connectivity of coseismic landsliding in the Gorkha event suggests coupling between the earthquake cycle and sediment/geochemical budgets of fluvial systems in the Himalaya.ISSN:0169-555xISSN:1872-695