Resulting Ground Motion Research Articles

Five key lessons gained from induced seismicity monitoring in western Canada

In response to induced seismicity observed in western Canada, existing public networks have been densified and a number of private networks have been deployed to closely monitor induced earthquakes associated with oil and gas operations in the region. Over the past three years, we generated an unprecedented volume of seismic data from monitoring induced seismicity for some of the most active operators in western Canada. This rich data set can be used to understand preexisting geologic structures, the activation mechanisms and probabilities, and seismological attributes of the resultant ground motions. Acknowledging that the primary goal of private networks is assisting operators in making operational decisions, these insights can play key roles in improving the accuracy of event magnitudes, ground-motion predictions, and hazard estimates, which successively can be used for developing effective risk management strategies.

A finite element and finite difference mixed approach for modeling fault rupture and ground motion

We combine a finite element (FE) code, Defmod, and a finite difference (FD) code, OpenSWPC, in modeling fault rupture and resulting ground motion. The rupturing process is modeled by the FE code, while the ground motion is modeled by the FD code. The FE-FD binding follows two steps: First, evaluate the FD grid points motion when executing the FE code; and then, impose those moving grid points to the FD domain to drive wave propagation. In order to avoid performance bottleneck, we implement this FE-FD binding in parallel. To verify this mixed approach, we evaluate two SCEC benchmark problems. The resulting synthetic waveforms agree well with the other benchmark participants. The waveform comparisons suggest that the FE-FD mixed model has less attenuation than the pure FE model.

Investigation of topographical effects on rupture dynamics and resultant ground motions

Investigation of topographical effects on rupture dynamics and resultant ground motions

Modification of stochastic ground motion models for matching target intensity measures

SummaryStochastic ground motion models produce synthetic time‐histories by modulating a white noise sequence through functions that address spectral and temporal properties of the excitation. The resultant ground motions can be then used in simulation‐based seismic risk assessment applications. This is established by relating the parameters of the aforementioned functions to earthquake and site characteristics through predictive relationships. An important concern related to the use of these models is the fact that through current approaches in selecting these predictive relationships, compatibility to the seismic hazard is not guaranteed. This work offers a computationally efficient framework for the modification of stochastic ground motion models to match target intensity measures (IMs) for a specific site and structure of interest. This is set as an optimization problem with a dual objective. The first objective minimizes the discrepancy between the target IMs and the predictions established through the stochastic ground motion model for a chosen earthquake scenario. The second objective constraints the deviation from the model characteristics suggested by existing predictive relationships, guaranteeing that the resultant ground motions not only match the target IMs but are also compatible with regional trends. A framework leveraging kriging surrogate modeling is formulated for performing the resultant multi‐objective optimization, and different computational aspects related to this optimization are discussed in detail. The illustrative implementation shows that the proposed framework can provide ground motions with high compatibility to target IMs with small only deviation from existing predictive relationships and discusses approaches for selecting a final compromise between these two competing objectives.

3D Effects of Sedimentary Wedges and Subsurface Canyons: Ground‐Motion Amplification in the Israeli Coastal Plain

Abstract We study the propagation of seismic waves, the resulting ground motions, and their amplification atop sedimentary structures underlying continental passive margins. We employ a set of generic models with increasing complexity within a framework of a 3D numerical scheme. The basic geological structure and velocity model were derived from the subsurface of the Israeli coastal plain where soft sediments form a wedge over the stiffer bedrock and fill subsurface canyons that incise deep into the bedrock. Ground motions were modeled for both seaside and landside seismic sources. We show that for a landside source, peak ground velocities (PGVs) atop a sedimentary wedge are amplified by a maximum factor of 2.6 and on average by a factor of 1.6, relative to a reference model. This amplification is mainly due to the ellipticity of Rayleigh waves in the soft sediment layer. Spatial distribution of amplification factors shows that sedimentary wedges do not exhibit a prominent edge effect. Atop sediment‐filled canyons and landside source, PGV are amplified by a maximum factor of 3.3, relative to a reference model, along the exposed part of the canyon. The PGV amplification factor in the canyon relative to adjacent hard‐rock site is up to 2.4. PGV amplification atop the sediment‐filled canyons is mainly due to the geometrical focusing of SH waves. Based on our findings, we present a simplified ground‐motion amplification map for the Israeli coastal plain. Electronic Supplement: Animations of the three components of the ground‐motion models.

Factors controlling high-frequency radiation from extended ruptures

Small-scale slip heterogeneity or variations in rupture velocity on the fault plane are often invoked to explain the high-frequency radiation from earthquakes. This view has no theoretical basis, which follows, for example, from the representation integral of elasticity, an exact solution for the radiated wave field. The Fourier transform, applied to the integral, shows that the seismic spectrum is fully controlled by that of the source time function, while the distribution of final slip and rupture acceleration/deceleration only contribute to directivity. This inference is corroborated by the precise numerical computation of the full radiated field from the representation integral. We compare calculated radiation from four finite-fault models: (1) uniform slip function with low slip velocity, (2) slip function spatially modulated by a sinusoidal function, (3) slip function spatially modulated by a sinusoidal function with random roughness added, and (4) uniform slip function with high slip velocity. The addition of “asperities,” both regular and irregular, does not cause any systematic increase in the spectral level of high-frequency radiation, except for the creation of maxima due to constructive interference. On the other hand, an increase in the maximum rate of slip on the fault leads to highly amplified high frequencies, in accordance with the prediction on the basis of a simple point-source treatment of the fault. Hence, computations show that the temporal rate of slip, not the spatial heterogeneity on faults, is the predominant factor forming the high-frequency radiation and thus controlling the velocity and acceleration of the resulting ground motions.

Seismic Source Modeling in the Shores of Western Makran

Makran is an active subduction zone with a lower activity rate in comparison with other similar subduction zones. In the extent of Makran seismotectonic province, from coastline up to 70 Km distance onshore, the earthquakes are shallow whilst further inland, focal depths of the earthquakes are deeper. Con-sidering the low seismic activity rate, lack of adequate and reliable seismic data and uncertainty about earthquake hazard contribution ratio of subduction segments and faults, it is intended in this article to determine the most accurate method of seismic source modelling. Estimation of the maximum strong ground motion in this province has been assessed by assuming various combinations of activity rate contribution ratios, i.e. independent activity of either subduction source or faults or simultaneous activity of subduction source and faults. According to the obtained results, the maximum and minimum limits of the strong ground motion acceleration is related to the independent seismic activity models and when subduction source and faults are assumed to be contributing simultaneously to the activity rate of the region, the resultant ground motion acceleration will be between the limits obtained based on independent activity models.

A probabilistic seismic hazard assessment for the Turkish territory—part I: the area source model

The seismic zoning map of Turkey that is used in connection with the national seismic design code (versions issued both in 1997 and 2007) is based on a probabilistic seismic hazard assessment study conducted more than 20 years ago (Gulkan et al. in En son verilere gore hazirlanan Turkiye deprem bolgeleri haritasi, Report No: METU/EERC 93-1, 1993). In line with the efforts for the update of the seismic design code, the need aroused for an updated seismic hazard map, incorporating recent data and state-of-the-art methodologies and providing ground motion parameters required for the construction of the design spectra stipulated by the new Turkish Earthquake Design Code. Supported by AFAD (Disaster and Emergency Management Authority of Turkey), a project has been conducted for the country scale assessment of the seismic hazard by probabilistic methods. The present paper describes the probabilistic seismic hazard assessment study conducted in connection with this project, incorporating in an area source model, all recently compiled data on seismicity and active faulting, and using a set of recently developed ground motion prediction equations, for both active shallow crustal and subduction regimes, evaluated as adequately representing the ground motion characteristics in the region. The area sources delineated in the model are fully parameterized in terms of maximum magnitude, depth distribution, predominant strike and dip angles and mechanism of possible ruptures. Resulting ground motion distributions are quantified and presented for PGA and 5 % damped spectral accelerations at T = 0.2 and 1.0 s, associated with return periods of 475 and 2475 years. The full set of seismic hazard curves was also made available for the hazard computation sites. The second part of the study, which is based on a fault source and smoothed seismicity model is covered in Demircioglu et al. in Bull Earthq Eng, (2016).

Site amplification in the Kathmandu Valley during the 2015 M7.6 Gorkha, Nepal earthquake

The 25th April 2015 M7.6 Gorkha earthquake caused significant damage to buildings and infrastructure in both Kathmandu and surrounding areas as well as triggering numerous, large landslides. This resulted in the loss of approximately 8600 lives. In order to learn how the impact of such events can be reduced on communities both in Nepal and elsewhere, the Earthquake Engineering Field Investigation Team (EEFIT) reconnaissance mission was undertaken, aiming to look at damage patterns within the country. Passive, microtremor recordings in severely damaged areas of the Kathmandu Valley, as well as at the main seismic recording station in Kathmandu (USGS station KATNP) are used to determined preliminary shear wave velocity (Vs) profiles for each site. These profiles are converted into spectral acceleration using the input motion of the Gorkha earthquake. The results are limited, but show clear site amplification within the Siddhitol Region. The resulting ground motions exceed the design levels from the Nepalese Building Codes, indicating the need for site-specific hazard analysis and for revision of the building code to address the effect of site amplification.

Development of integrated earthquake simulation system for Istanbul

Recent advances in computing have brought a new and challenging way to tackle the earthquake hazard and disaster problems: integration of the seismic actions in the form of numerical models. For this purpose, integrated earthquake simulation (IES) has been developed in Japan, and now a new version is being developed in Turkey which targets Istanbul. This version of IES is being built in MATLAB and includes site response analysis and structural analysis of existing buildings with data obtained via GIS databases. In this study, we present an initial application in Zeytinburnu district of Istanbul where the results are expressed in the form of spatial distributions of ground motion and building responses. At the end of the analysis, it is seen that most of the buildings make small displacements and the displacement values are directly proportional to the total height of the structures. Since the obtained ground motion distribution and peak values are not very high, structural damage has not been observed under the current simulation. The effect of bedrock depth and soil parameters on strong ground motion distribution has been observed. The most effective ground motion locations in the selected area have been determined, and the critical buildings that have maximum displacement during the earthquake motion are detected. Currently, the IES on MATLAB does not include the source to bedrock wave propagation mechanism and the resulting ground motions at each grid point. In future studies, alternative models for this purpose along with input model parameters for Istanbul will be applied. Once the source-to-structure integrated model is complete, past earthquakes as well as potential scenario events in Istanbul will be modeled in the final form of IES on MATLAB. Results will be valuable for a variety of purposes ranging from disaster mitigation to emergency management. In future part of this study, site vibration tests will also be made for buildings that do not comply with seismic design codes and constitute the largest portion of the seismic risk. New models will be developed for these buildings and adopted into the IES system.

Kinematic source models for long-period ground motion simulations of megathrust earthquakes: validation against ground motion data for the 2003 Tokachi-oki earthquake

In this study, a method for simulating the ground motion of megathrust earthquakes at periods of approximately 2 s and longer was validated by using the characterized source model combined with multi-scale spatial heterogeneity. Source models for the M W 8.3, 2003 Tokachi-oki earthquake were constructed, and ground motion simulations were conducted to test their performance. First, a characterized source model was generated based on a source model obtained from waveform inversion analysis. Then, multi-scale heterogeneity was added to the spatial distribution of several source parameters to yield a heterogeneous source model. An investigation of the Fourier spectra and 5 % damped velocity response spectra of the simulated and observed ground motions demonstrated that adding multi-scale heterogeneity to the spatial distributions of the slip, rupture velocity, and rake angle of the characterized source model is an effective method for constructing a source model that explains the ground motion at periods of 2–20 s. It was also revealed how the complexity of the parameters affects the resulting ground motion. The complexity of the rupture velocity had the largest influence among the three parameters.

Correlative relationships between tsunami height and strong ground motion parameters: Japanese earthquakes

When a large earthquake occurs off a coast, the resulting ground motion can soon be followed by the arrival of tsunami waves. This interrelationship can be useful for issuing tsunami alerts. This study aims at detecting correlative relationships between the intensity (runup) of a tsunami at a site along the coast and ground motion parameters at the same site due to the earthquake that produced the tsunami. Our estimates were derived by combining historical and instrumental data for eight sites along the Pacific coast of Japan. Our regression analysis of collected and systematized data used the tobit model, which is able to incorporate all tsunami data, including those below the tsunami-detection threshold. We show that if such tsunamis are neglected by the standard regression model, the result is to overestimate the height of predicted tsunamis. Analysis of the regression results shows that when a tsunami-generating earthquake has occurred a tsunami with runup that is equal to or greater than 50 cm should be expected if peak ground motion velocities greater than 7 cm/s have been recorded at the same site, with the probability of the failure to predict being 16%.

Rupture and Ground‐Motion Models on the Northern San Jacinto Fault, Incorporating Realistic Complexity

We use the 3D finite‐element method to conduct dynamic models of rupture and resulting ground motion on the Claremont–Casa Loma stepover of the northern San Jacinto fault. We incorporate complex fault geometry (from the U.S. Geological Survey [USGS] Quaternary Faults Database; see [Data and Resources][1]), a realistic velocity structure (the Southern California Earthquake Center Community Velocity Model‐S), a realistic regional stress field with an orientation taken from seismicity relocation literature, and several stochastic self‐similar shear stress distributions. As we incorporate more types of complexity, the specific effects of any individual factor become less apparent within the overall rupture behavior. We also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates. Using a regional stress field alone, as well as with the combined regional and stochastic stress realization, we find that the stepover presents a significant barrier to rupture, regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment. Greater heterogeneity of stresses tends to produce shorter ruptures. Within this result, we find that the Claremont strand is more favorable for long ruptures than the Casa Loma–Clark strand. Low‐frequency ground‐motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity. The strongest motions produced in these models are in the San Bernardino basin. Although directivity effects do contribute to the low‐frequency ground‐motion distribution, particularly in the near field, they are secondary to the effects of the velocity structure. Online Material: Figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation. [1]: #sec-18

A Monte Carlo Method for Probabilistic Hazard Assessment of Induced Seismicity due to Conventional Natural Gas Production

Abstract A Monte Carlo approach to probabilistic seismic‐hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalog. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a probabilistic representation of the ground‐motion hazard. This approach is particularly well suited to the specific nature of the time‐dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the Groningen gas field. A new ground‐motion prediction equation (GMPE) tailored to the Groningen field has been derived by calibrating an existing GMPE with local strong‐motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0.57 g and a 2% chance of exceeding a peak ground velocity of 22 cm/s above the area of maximum compaction. Disaggregation shows that earthquakes of M w 4–5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

Computational modeling of buried blast-induced ground motion and ground subsidence

To complement the method of field-scale seismic ground motion simulations by buried blast techniques, the application and evaluation of the capability of a numerical modeling platform to simulate buried explosion-induced ground motion at a real soil site is presented in this paper. Upon a layout of the experimental setup at a level site wherein multiple charges that were buried over a large-diameter circle and detonated in a planned sequence, the formulation of a numerical model of the soil and the explosives using the finite element code LS-DYNA is developed for the evaluation of the resulting ground motion and surface subsidence. With a compact elastoplastic cap model calibrated for the loess soils on the basis of the site and laboratory test program, numerical solutions are obtained by explicit time integration for various dynamic aspects and their relation with the field blast experiment. Quantitative comparison of the computed ground acceleration time histories at different locations and induced spatial subsidence on the surface afterwards is given for further engineering insights in regard to the capabilities and limitations of both the numerical and experimental approaches.

Rupture Propagation and Ground Motion of Strike‐Slip Stepovers with Intermediate Fault Segments

Field studies of historic rupture traces show that fault stepovers commonly serve as endpoints to earthquake ruptures. This is an effect that is corroborated by past dynamic modeling studies. However, field studies also show a great deal of complexity in fault‐zone structure within a stepover, which is often simplified out of modeling studies. In the present study, we use the 3D finite‐element method to investigate the effect of one type of smaller‐scale complexity on the rupture process: a smaller fault segment positioned between the two primary strands of a strike‐slip fault stepover. We find that such small faults can have a controlling effect on whether or not a rupture is able to jump the stepover and on the resulting ground motions from these ruptures. However, this effect is neither straightforward nor linear: the length of the intermediate segment and its basal depth, as well as whether the stepover is extensional or compressional, all contribute to the rupture behavior and ground‐motion distribution. These results have important implications for assessing the probability of a rupture propagating through small‐ and large‐scale discontinuities in faults, as well as for evaluating ground‐motion intensities near fault stepovers. Because of the sensitivity of results to so many parameters, these results also suggest that modeling studies on idealized fault geometries may not be sufficient to describe the rupture behaviors of specific complex fault systems. Site‐specific modeling studies, where possible, will provide better inputs and constraints for probabilistic rupture length assessments as well as for ground‐motion estimates.

Modeling Earthquakes Using Fractal Circular Patch Models with Lessons from the 2011 Tohoku-Oki Earthquake

Earthquakes occur in a complex hierarchical fault system, meaning that a realistic mechanically-consistent model is required to describe heterogeneity simply and over a wide scale. We developed a simple conceptual mechanical model using fractal circular patches associated with fracture energy on a fault plane. This model explains the complexity and scaling relation in the dynamic rupture process. We also show that such a fractal patch model is useful in simulating longterm seismicity in a hierarchal fault system by using external loading. In these studies, an earthquake of any magnitude appears as a completely random cascade growing from a small patch to larger patches. This model is thus potentially useful as a benchmarking scenario for evaluating probabilistic gain in probabilistic earthquake forecasts. The model is applied to the real case of the 2011 Tohoku-Oki earthquake based on prior information from a seismicity catalog to reproduce the complex rupture process of this very large earthquake and its resulting ground motion. Provided that a high-quality seismicity catalog is available for other regions, similar approach using this conceptual model may provide scenarios for other potential large earthquakes.

A 2D Pseudodynamic Rupture Model Generator for Earthquakes on Geometrically Complex Faults

Abstract Geologic observations indicate that faults are fractally rough surfaces, with deviations from planarity at all length scales. Fault roughness introduces complexity in the rupture process and resulting ground motion. We present a 2D kinematic rupture generator that emulates the strong dependence of earthquake source parameters on local fault geometry observed in dynamic models of ruptures on nonplanar faults. This pseudodynamic model is based on a statistical analysis of ensembles of 2D plane strain rupture simulations on fractally rough faults with rate‐weakening friction and off‐fault viscoplasticity. We observe strong anticorrelation of roughness‐induced fluctuations in final slip, rupture velocity, and peak slip velocity with the local fault slope for right‐lateral strike‐slip ruptures. Spatial variability in these source parameters excites high‐frequency seismic waves that are consistent with observed strong‐motion records. Although accurate modeling of this high‐frequency motion is critical to seismic‐hazard analysis, dynamic rupture simulations are currently too computationally inefficient to be of practical use in such applications. We find that the seismic waves excited by the pseudodynamic model have similar intensity and spectral content to the corresponding dynamic model. Although the method has been developed in 2D, we envision that a similar approach could be taken for the 3D problem, provided that computational resources are available to generate an ensemble set of 3D dynamic rupture simulations. The resulting methodology is expected to find future application in efficient earthquake simulations that accurately quantify high‐frequency ground motion.

Research of Earthquake Topographic Effect

In this paper, the influence of topography on ground-motion intensity parameter, response spectrum, peak ground acceleration (PGA) and the ratio of response spectrum were studied based on the measured data from large scale shaking table test and observation stations in XiShan park for Wenchuan earthquake. The results show that: in the EW direction, the height do not affect PGD, SMA, VSI and HI, while V_RMS decreases slightly at the middle of the slope, the other intensity parameters increase with the increase of height. In the EW direction, the height has no influence on PGD, V_RMS, SMA, SED, A_RMS, VSI and HI, while other parameters increase as the height increase. In the UD direction, the height has no influence on SMV, PGD, V_RMS, SMV, ASI, VSI and HI, while A_RMS decreases at the middle of the slope, and the other intensity parameters increase as the height increase. Ignoring the local topographic effect, the amplitude of response spectrum increases with the increase of height at the part of short period (T1s), the part of long period (T>1s) is not effected by height. The ground motion will be amplified by local canyon topography, and the influence of local topography is larger than height. The research carried out in paper will deepen the understanding of topographic effect. 0 Preface Earthquake often cause extensive rock slope failures and various types of mass movement in mountainous areas. Catastrophic seismically-induced landsides are among the Earths most powerful geomorphic events, causing sudden and dramatic changes to the landscape, creating high risks to both infrastructures and life, and reputedly causing large economic losses. Seismic waves interacting with topography lead to amplification and deamplification of resulting ground motion. In the western mountainous areas of China, the topography is extremely complex, many large hydropower stations were built in narrow valleys and many large bridge piers were built on valleys and hillsides, so the research about topographic effect is essential to the seismic design of large-scale projects. Topographic effect is always analyzed with following three approaches: motion observation, analytical analysis and numerical analysis. The motion observation is regarded as the most efficient and common approach [1]. Long time ago, the researchers found that the intensity of buildings built on local convex topography was abnormal, in order to reveal the reason of abnormal intensity, array stations were constructed specially to study the effect of local convex topography on ground motion, some observation data were obtained. Some L-7 type strong motion seismographs were installed at the crest and foot of Kagel and Josephine mountain, California, by Lawrence L. Davis and Lewis R. West, the 2 array stations had recorded several aftershocks record of SanFernando earthquake, which occurred on February 9, 1971[. Some L-7 type strong motion seismographs were also installed at the crest, hillside and foot of Butler mountain, Nevada, to record blasting vibration in test site. In 1984, in order to observe the topographic effect of rocky mountain, 8 observation stations were installed by B. E. Tucker, five stations were placed in two tunnels with different elevation, the other three were placed at the surface of outcropped rock [. After the 1989 Loma prieta earthquake, dense array stations of seven digital and triaxial seismographs were mounted on Robinwood Ridge, which is located at 7.3km northwest of epicenter, to analyze the reason of seriously damage on high-strength buildings and cracks of ground [4,. In China, a earthquake observation station was constructed in XiShan Park, ZiGong, SiChuan province in 2007, which recorded the main acceleration time history of WenChuan earthquake perfectly, the establishment of this station offers valuable data to researchers for exploring the local topographic effect on ground motion [6]. In 2010, a research was conducted by Wang Haiyun and Xie Lili with traditional spectral ratio method, some significant conclusions were drawn about the influence of topographic effect on ground motion [7]. In this paper, WenChuan seismic wave was analyzed in time and frequency domain to explore the influence of topography on ground-motion intensity parameters, response spectrum and spectrum characteristic.

Probabilistic seismic hazard analysis in Nepal

The seismic ground motion hazard for Nepal has been estimated using a probabilistic approach. A catalogue of earthquakes has been compiled for Nepal and the surrounding region (latitude 26° N and 31.7° N and longitude 79° E and 90° E) from 1255 to 2011. The distribution of catalogued earthquakes, together with available geological and tectonic information were used to delineate twenty-three seismic source zones in Nepal and the surrounding region. By using the seismic source information and probabilistic earthquake hazard parameters in conjunction with a selected ground motion prediction relationship, peak ground accelerations (PGAs) have been calculated at bedrock level with 63%, 10%, and 2% probability of exceedance in 50 years. The estimated PGA values are in the range of 0.07–0.16 g, 0.21–0.62 g, and 0.38–1.1 g for 63%, 10%, and 2% probability of exceedance in 50 years, respectively. The resulting ground motion maps show different characteristics of PGA distribution, i.e., high hazard in the far-western and eastern sections, and low hazard in southern Nepal. The quantified PGA values at bedrock level provide information for microzonation studies in different parts of the country.