Environmental Impact Assessment and Seismic Hazard Analysis: Petrinja 2020 Experience

SUMMARYOn 29 December 2020, a shallow earthquake of magnitude Mw 6.4 struck northern Croatia, near the town of Petrinja, more than 24 hr after a strong foreshock (ML 5). We formed a reconnaissance team of European geologists and engineers, from Croatia, Slovenia, France, Italy and Greece, rapidly deployed in the field to map the evidence of coseismic environmental effects. In the epicentral area, we recognized surface deformation, such as tectonic breaks along the earthquake source at the surface, liquefaction features (scattered in the fluvial plains of Kupa, Glina and Sava rivers), and slope failures, both caused by strong motion. Thanks to this concerted, collective and meticulous work, we were able to document and map a clear and unambiguous coseismic surface rupture associated with the main shock. The surface rupture appears discontinuous, consisting of multi-kilometre en échelon right stepping sections, along a NW–SE striking fault that we call the Petrinja-Pokupsko Fault. The observed deformation features, in terms of kinematics and trace alignments, are consistent with slip on a right lateral fault, in agreement with the focal solution of the main shock. We found mole tracks, displacement on faults affecting natural features (e.g. drainage channels), scarplets and more frequently breaks of anthropogenic markers (roads, fences). The surface rupture is observed over a length of ∼13 km from end-to-end, with a maximum displacement of 38 cm, and an average displacement of ∼10 cm. Moreover, the liquefaction extends over an area of nearly 600 km2 around the epicentre. Typology of liquefaction features include sand blows, lateral spreading phenomenon along the road and river embankments, as well as sand ejecta of different grain size and matrix. Development of large and long fissures along the fluvial landforms, current or ancient, with massive ejections of sediments is pervasive. These features are sometimes accompanied by small horizontal displacements. Finally, the environmental effects of the earthquake appear to be reasonably consistent with the usual scaling relationships, in particular the surface faulting. This rupture of the ground occurred on or near traces of a fault that shows clear evidence of Quaternary activity. Further and detailed studies will be carried out to characterize this source and related faults in terms of future large earthquakes potential, for their integration into seismic hazard models.

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

The USGS is currently leading an effort to compile published geological information on Quaternary faults, folds, and earthquake-induced liquefaction in order to develop an internally consistent database on the locations, ages, and activity rates of major earthquake-related features throughout the United States. This report is the compilation for such features in the Central and Eastern United States (CEUS), which for the purposes of the compilation, is defined as the region extending from the Rocky Mountain Front eastward to the Atlantic seaboard. A key objective of this national compilation is to provide a comprehensive database of Quaternary features that might generate strong ground motion and therefore, should be considered in assessing the seismic hazard throughout the country. In addition to printed versions of regional and individual state compilations, the database will be available on the World-Wide Web, where it will be readily available to everyone. The primary purpose of these compilations and the derivative database is to provide a comprehensive, uniform source of geological information that can by used to complement the other types of data that are used in seismic-hazard assessments. Within our CEUS study area, which encompasses more than 60 percent of the continuous U.S., we summarize the geological information on 69 features that are categorized into four classes (Class A, B, C, and D) based on what is known about the feature's Quaternary activity. The CEUS contains only 13 features of tectonic origin for which there is convincing evidence of Quaternary activity (Class A features). Of the remaining 56 features, 11 require further study in order to confidently define their potential as possible sources of earthquake-induced ground motion (Class B), whereas the remaining features either lack convincing geologic evidence of Quaternary tectonic faulting or have been studied carefully enough to determine that they do not pose a significant seismic hazard (Classes C and D). The correlation between historical seismicity and Quaternary faults and liquefaction features in the CEUS is generally poor, which probably reflects the long return times between successive movements on individual structures. Some Quaternary faults and liquefaction features are located in aseismic areas or where historical seismicity is sparse. These relations indicate that the record of historical seismicity does not identify all potential seismic sources in the CEUS. Furthermore, geological studies of some currently aseismic faults have shown that the faults have generated strong earthquakes in the geologically recent past. Thus, the combination of geological information and seismological data can provide better insight into potential earthquake sources and thereby, contribute to better, more comprehensive seismic-hazard assessments.

Present‐day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike‐slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE‐directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre‐Early Pleistocene D1 event of NE‐trending compression, which gave rise to the large‐scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan‐Azua basin. This was followed by a near pure strike‐slip D2 stress regime, partitioned into the N‐S to NE‐SW transverse Ocoa‐Bonao‐La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub‐parallel deformation corridors. Shift to D2 strike‐slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard.

Section 1: Earthquake Source.- Strong Motion Seismology.- Earthquake Source Mechanisms: Case Studies.- Source Parameters of Some Friuli Earthquakes (1976-1977) From Strong Motion Data.- The Seismic Inverse Problem For a Flat Structure.- Section 2: Prediction of Strong Ground Motion.- The Prediction of Strong Ground Motion.- A Theoretical Study of the Dependence of the Peak Ground Acceleration on Source and Structure Parameters.- Numerical Simulation of Earthquake Ground Motion.- High Frequency Earthquake Strong Ground Motion in Laterally Varying Media: The Effect of a Fault Zone.- Physical Mechanisms Contributing to Seismic Attenuation in the Crust.- Section 3: Acquisition and Interpretation of Strong Motion Data (Including Case Histories).- Data Acquisition and Processing in Strong Motion Seismology.- Strong Ground Motions in Italy: Accelerogram Spectral Properties and Prediction of Peak Values.- Analysis of Strong-Motion Data From the New Hampshire Earthquake of 18 January 1982.- Seismic Intensity and its Applications to Engineering: A Study in Japan.- Seismic Intensity and its Applications to Engineering: A Study in Turkey.- Section 4: Hazard Assessment.- Probabilistic Models for Assessment of Strong Ground Motion.- Seismic Source Regionalization.- Section 5: Site Response and Engineering Application.- Site Response Analysis.- Constitutive Relationships for Soil Dynamics.- Source and Local Site Effects-Preliminary Results Based on the Friuli Earthquake Sequence 1976.- Soil Structure Interaction Effects on Strong Ground Motion.- Engineering Uses of Strong Motion Data.

<p>Earthquakes and related coseismic effects at the surface, both primary and secondary, such as liquefaction and lateral spreading, can impact humans due to induced economic or social disruptions (e.g. slope, bridge and building foundation failures, flotation of buried structures). In this respect, it results of primary interest to map liquefaction induced evidences soon after an earthquake. On the 29th December 2020, a major earthquake (Mw 6.4) occurred in Croatia, close to Petrinja, 45 km south of Zagreb, generating widespread liquefaction and lateral spreading phenomena in a radius of approximately 20 km from the epicentre. A European team of researchers (geologists and engineers), in strict collaboration with the Croatian Geological Survey, performed field reconnaissance campaigns with the aim to provide a detailed identification and characterization of the primary and secondary geological and geotechnical coseismic effects induced by the Croatian earthquakes. Specifically with reference to the liquefaction phenomena, the Working Group integrated the data collected directly in the field with those from remote survey by drone aerial photos acquired in the post-event immediate. The adopted process allowed the collection of the liquefaction record with the highest possible completeness both in terms of pattern and distribution of the phenomena. The database includes several detailed case studies typified by the following characteristics: (1) liquefaction occurring on alluvial plain sites (Kupa river, Sava river and Glina river); (2) blows made by sand and/or gravel with local presence of shells and armored mud balls; (3) lateral spreading phenomena along road and river embankments; (4) sand ejecta of different grain size and matrix, even at the same site; (5) sand and/or gravel ejecta along fault traces. The characteristics of these features are discussed with reference to the alluvial setting and tectonic context. All together, the detailed survey of these recent liquefaction features will assist to build new empirical relations, to update the existing ones and to mitigate the effects of future earthquakes recognizing liquefaction prone areas for a correct land use planning, as for seismic microzonation studies.</p>

Abstract. Italy is one of the most seismically active countries in Europe. Moderate to strong earthquakes, with magnitudes of up to ∼ 7, have been historically recorded for many active faults. Currently, probabilistic seismic hazard assessments in Italy are mainly based on area source models, in which seismicity is modelled using a number of seismotectonic zones and the occurrence of earthquakes is assumed uniform. However, in the past decade, efforts have increasingly been directed towards using fault sources in seismic hazard models to obtain more detailed and potentially more realistic patterns of ground motion. In our model, we used two categories of earthquake sources. The first involves active faults, and using geological slip rates to quantify the seismic activity rate. We produced an inventory of all fault sources with details of their geometric, kinematic, and energetic properties. The associated parameters were used to compute the total seismic moment rate of each fault. We evaluated the magnitude–frequency distribution (MFD) of each fault source using two models: a characteristic Gaussian model centred at the maximum magnitude and a truncated Gutenberg–Richter model. The second earthquake source category involves grid-point seismicity, with a fixed-radius smoothed approach and a historical catalogue were used to evaluate seismic activity. Under the assumption that deformation is concentrated along faults, we combined the MFD derived from the geometry and slip rates of active faults with the MFD from the spatially smoothed earthquake sources and assumed that the smoothed seismic activity in the vicinity of an active fault gradually decreases by a fault-size-driven factor. Additionally, we computed horizontal peak ground acceleration (PGA) maps for return periods of 475 and 2475 years. Although the ranges and gross spatial distributions of the expected accelerations obtained here are comparable to those obtained through methods involving seismic catalogues and classical zonation models, the spatial pattern of the hazard maps obtained with our model is far more detailed. Our model is characterized by areas that are more hazardous and that correspond to mapped active faults, while previous models yield expected accelerations that are almost uniformly distributed across large regions. In addition, we conducted sensitivity tests to determine the impact on the hazard results of the earthquake rates derived from two MFD models for faults and to determine the relative contributions of faults versus distributed seismic activity. We believe that our model represents advancements in terms of the input data (quantity and quality) and methodology used in the field of fault-based regional seismic hazard modelling in Italy.

The 12 research papers and two summaries of conference discussion sessions contained in this Theme Issue build upon presentations and dialogue at the Third Johnston–Lavis Colloquium held at University College London in September 2009. The meeting brought together delegates from the UK, Europe and

Landslides often occur as a consequence of natural hazards among which earthquakes are one of the main triggering factors. The effects of earthquake-induced ground shaking are often sufficient to cause the failure of slopes that were marginally to moderately stable before the earthquake. In this study, we define screening maps for Italy that classify sites in terms of their potentiality of triggering earthquake-induced landslides based on seismic hazard. To this end, we analyze seismic hazard maps and hazard disaggregation results on a national scale. First, as instabilities occur for acceleration values exceeding critical acceleration, we compare surface peak ground acceleration values derived from national hazard maps with critical acceleration thresholds proposed in the scientific literature. Then, magnitude-distance (M-R) scenarios from hazard disaggregation are analyzed in relation to upper-bound M-R curves for seismic landslide triggering. Landslide triggering can not be discounted if the value of the source-to-site distance R associated with magnitude M is lower than the reference upper-bound value and surface peak ground acceleration exceeds a given critical acceleration value.Most of the work concerns the analysis of hazard disaggregation results to define the controlling M-R scenarios. First, joint probability mass functions (PMFs) of magnitude and distance are analyzed to identify all modal scenarios (i.e., local maxima). To this end, we treat each PMF as an image and apply morphological image processing techniques to find local maxima. Specifically, the maximum (dilation) filter operation is applied. Local maxima are detected by checking for element-wise equality between the original and filtered matrices. Then, for each computation node, mean and modal M-R scenarios are compared to upper-bound M-R curves for earthquake-induced landslides selected from the scientific literature and the preferred M-R pair is selected as follows:if all M-R pairs stand above the reference upper-bound curve, then the triggering of earthquake-induced landslides can be neglected. if at least one M-R pair is below the reference upper-bound curve, then the triggering of earthquake-induced landslides can not be discounted. if more than one M-R pair lies below the reference upper-bound curve, then the triggering of earthquake-induced landslides can not be excluded and the M-R scenario that contributes the most to the hazard (i.e., the M-R pair with the largest PMF value) is selected as the preferred magnitude. As sites respond at specific characteristic frequencies (depending on local geological characteristics) and disaggregation results may vary with response period (T), the previous procedure is repeated considering disaggregation results associated with different spectral periods (i.e., spectral acceleration for different response periods). This allows us to define the controlling M-R pair for each site in relation to geological conditions (through site classification).The entire workflow is replicated for three types of landslides (disrupted slides and falls, coherent slides, and lateral spreads and flows), thus leading to three maps that show areas in Italy where the triggering of landslides due to seismic activity can not be excluded. The reliability of our results is finally checked by comparing them with observations of past seismic landslides in Italy.

To carry out a realistic simulation of earthquake strong ground motion for applied studies, one needs an earthquake fault/source simulator that can integrate most relevant features of observed earthquake ruptures. A procedure of this kind is proposed that creates a broadband kinematic source model. At lower frequencies, the source is described as propagating slip pulse with locally variable velocity. The final slip is assumed to be a two-dimensional (2D) random function. At higher frequencies, radiation from the same running strip is assumed to be random and incoherent in space. The model is discretized in space as a grid of point subsources with certain time histories. At lower frequencies, a realistic shape of source spectrum is generated implicitly by simulated kinematics of slip pulse propagation. At higher frequencies, the original approach is used to generate signals with spectra that plausibly approximate the prescribed smooth far-field source spectrum. This spectrum is set on the basis of the assumedly known regional empirical spectral scaling law, and subsource moment rate time histories are conditioned so as to fit this expected spectrum. For the random function that describes final slip over the fault area, lognormal probability distribution of amplitudes is assumed, on the basis of exploratory analysis of inverted slip distributions. Similarly, random functions that describe local slip rate time histories are assumed to have lognormal distribution of envelope amplitudes. In this way one can effectively emulate expressed “asperities” of final slip and occasional occurrence of large spikes on near-source accelerograms. A special procedure is proposed to simulate the spatial coherence of high-frequency fault motion. This approach permits the simulation of fault motion plausibly at high spatial resolution, fulfilling the prerequisite for simulation of strong motion in the vicinity of a fault. A particular realization (sample) of a source created in a simulation run depends on several random seeds, and also on a considerable number of parameters. Their values can be selected so as to take into account expected source features; they can also be perturbed to examine the source-related component of uncertainty of strong motion. The proposed approach to earthquake source specification is well adapted to the study of deterministic seismic hazard: it may be used for simulation of individual scenario events, or suites of such events, as well as for analysis of uncertainty for expected ground motion parameters from a particular class of events. Examples are given of application of the proposed approach to strong motion simulations and related uncertainty estimation.

We simulate strong ground motions during the 1948 Fukui earthquake with the JMA magnitude 7.1 based on a heterogeneous source model and the hybrid simulation technique. So far there are no existing source models available for simulating strong ground motions from the 1948 Fukui earthquake. Most of the source models have been assumed to have uniform slip distribution on rectangular fault plane. Such models could generate ground motions only available longer than several seconds, underestimating shorter period motions (<1sec) of engineering interest. The objective of this paper is to construct a heterogeneous source model for simulating strong ground motions in a broad period band during the 1948 Fukui earthquake. We assume two source models to examine: Model 1 is a reverse fault model determined from the analysis of geodetic data by YOSHIOKA (1974) and Model 2 is a normal fault model from strong motion displacement data by KIKUCHI et al. (1999). Heterogeneous slip distribution on fault plane is estimated based on the self-similar scaling relationships of seismic moment versus asperity areas and slips by Somerville et al. (1999). Then we obtained the standardized source model consisting of two asperities to have the average characteristics of asperities for the seismic moment of the Fukui earthquake. Relative locations and rupture times of the asperities on the fault plane are determined following the source model by KIKUCHI et al. (1999). The maximum asperity corresponding to the second event in their model has an area of 12×12km2 and slip of 1.7m and is located under the most heavily damaged area along the buried fault, known as the Fukui earthquake fault. The smaller asperity corresponding to the first event is located north of the maximum asperity. Rupture was initiated at the northern edge of the smaller asperity, propagated toward south, then broke to start the maximum asperity 7 seconds after the initial rupture. Large ground motions from both models, Model 1 and 2, are spread over the Fukui basin, although peak velocity distributions are rather different between the two models. Areas over 30% collapse ratio during the Fukui earthquake correspond to those with peak velocity over 60cm/s for Model 1 and over 80cm/s for Model 2. The level of the peak velocity in the areas with more than 30% collapse ratio are estimated to be over 80cm/s connected with both results by MOROI et al. (1998) and MIYAKOSHI and HAYASHI (1998). Pseudo velocity response spectra in the center of the Fukui basin for Model 2 have almost the same level of the observed ones at Takatori (TKT) and the simulated ones at Fukuike (FKI) within the damage belt during the 1995 Hyogo-ken Nanbu earthquake. We conclude that the damage distribution during the Fukui earthquake is well explained by strong ground motions simulated for Model 2 combined with the normal fault model by KIKUCHI et al.. (1999) and a standardized heterogeneous source model developed by SOMERVILLE et al. (1999).

Preface and Acknowledgments. Report Adopted by the Workshop. Part 1: Seismic Hazard and Extreme Motions. Data Needs for Improved Seismic Hazard Analysis J.G. Anderson et al. Capturing and Limiting Ground-Motion Uncertainty in Seismic Hazard Assessment J.J. Bommer and F. Scherbaum. Long-Period Ground Motions from Digital Acceleration Recordings: A New Era in Engineering Seismology D.M. Boore. Observed Ground Motions, Extreme Ground Motions, and Physical Limits to the Ground Motions T.C. Hanks et al. Part 2: Engineering Uses of Strong Motion Seismograms. Raised Drift Demands for Framed Buildings during Near Field Earthquakes P. Gulkan and U. Yazgan. Impact of Near Fault Pulses on Engineering Design H. Krawinkler et al. Rapid Assessment of Building Response Using Generalized Interstory Drift Spectra E. Miranda and S. Akkar. Influence of Ground Motion Intensity on the Performance of Low- and Mid-Rise Ordinary Concrete Buildings S. Akkar et al. Part 3: Arrays and Observations. Integrated Surface and Borehole Strong-Motion, Soil-Response Arrays in San Francisco, California R.D. Borcherdt et al. Structural Monitoring Arrays - Past, Present and Future M. Celebi. Development of Strong-Motion Observation Network Constructed by NIED S. Kinoshita. Dense Strong-Motion Array in Yokohama, Japan, and Its Use for Disaster Management S. Midorikawa. The Cosmos Virtual Data Center R. Archuleta et al. Site-Dependent Groundmotion Data Recorded by German Taskforce in Turkey J. Schwarz et al. Observation and Prediction of Strong Ground Motion in China T. Xiaxin et al. Strong Motion Instrumentation Programs in Taiwan Yi-B. Tsai and Ch.P. Lee. Strong Motion Data Acquisition, Processing and Utilization with Applications to Istanbul Strong Motion Network M. Erdik et al. Addresses of Principal Contributors. Index.

Strong ground acceleration seismic hazard in Greece and neighboring regions

Seismicity, deformation and seismic hazard in the western rift of Corinth: New insights from the Corinth Rift Laboratory (CRL)

In Poland, underground mines of copper ores, which belong to KGHM Polish Copper JSC, have been struggling with seismic dynamic events such as tremors and rock bursts since almost the first years of exploitation i.e. the 70s of the twentieth century. Mining activities infringe the original stress balance and make the rock mass accumulate energy and then release it, which triggers seismic hazard even far away from a tremor epicentre. Therefore, prediction of the position, time and energy of tremors plays a significant role in mining operation especially in work safety. For this purpose, many observation methods including seismology, seismic, geotechnical-geological monitoring, are used; unfortunately, most of them help describe the state of the rock mass after but not prior to the occurrence of the seismic phenomena. Only passive seismic tomography is promising since it can be used to forecast, to some extent, the location of places of seismic energy excessive accumulation. In this method, on the basis of seismic events recorded in a given period, zones of high and low seismic wave velocity are determined (calculated), which in the near future may pose areas of increased seismic activity. The phenomenon of the increase of seismic longitudinal wave velocity with the increase of stress in rocks makes the ground of tomography calculations. The prime purpose of the paper is to assess passive seismic tomography as a means for forecasting and evaluation of seismic and rock burst hazard. To accomplish this, the analysis of seismic activity and archival seismic tomography results (seismic wave velocity zones and seismic anomaly zones) with reference to seismic phenomena, their energy, number and location were carried out. On the basis of obtained the results, the effectiveness of seismic hazard forecast with the use of passive seismic tomography was assessed. The research was carried out for one mining division of the Polkowice-Sieroszowice mine and covered ten years. This division was selected due to its high seismic activity and the permanent use of the passive seismic tomography to assess the seismic risk. Linear correlation and determination coefficients between seismic activity characteristics and seismic anomaly as well as longitudinal wave velocity were calculated. It was found that in the study area the effectiveness of passive seismic tomography in forecasting the seismic hazard is relatively satisfying since about half of the tremors were located within zones of high seismic activity (substantial velocity of P-waves and seismic positive anomalies)..