Local Seismicity Research Articles

Calibration of Local Magnitude Scale for Colombia

ABSTRACTNew calibration for local magnitude (ML) was performed for Colombia. The territory was divided into five zones using reported attenuation values for different areas of the country and correlating this information with the mapped lithologies, the absence or presence of volcanic activity, and patterns in the hypocentral locations of seismicity. Seismic data from the Colombian National Seismic Network—Colombian Geological Survey (RSNC-SGC) were used to obtain a total of 81,232 peak amplitudes from 22,816 earthquakes recorded between January 2015 and August 2017. This set of data was incorporated into a linear inversion to calculate the distance-correction functions for each zone. A new methodology is proposed for calculating the base level of the distance-correction function or parameter c, using the amplitude values for earthquakes with moment magnitudes (Mw) close to 3 measured at stations at distances close to 100 km. The distance-correction logA0 functions obtained in this study for the five zones are: Zone 1:−logA0=1.245×log(r)+0.0024×r−2.051,Zone 2:−logA0=1.056×log(r)+0.0021×r−1.76,Zone 3:−logA0=1.07×log(r)+0.0013×r−1.531,Zone 4:−logA0=1.241×log(r)+0.0015×r−2.178,Zone 5:−logA0=0.711×log(r)+0.0009×r−0.69, in which r is the hypocentral distance in kilometers. The results of this study are in use in the RSNC-SGC since September 2018. Before using the equations presented here, the values of local magnitude were previously underestimated for the entire Colombian territory. This work allows the calculation of the local magnitude using the largest attenuation changes in addition to decreasing discrepancies with other magnitude types such as Mw and those calculated by international networks.

The 1951 eruption of Mount Lamington, Papua New Guinea: Devastating directed blast triggered by small-scale edifice failure

The catastrophic explosion of Mount Lamington volcano, Papua New Guinea on January 21, 1951 produced a devastating pyroclastic density current (PDC) that knocked down dense tropical rainforest over an area of 230 km2 and killed approximately 3000 people. We present results of a field reinvestigation of the 1951 PDC deposit combined with an analysis of the available photographs and eyewitness accounts of the eruption first published in the fundamental work of G. A. M. Taylor (1958).We have concluded that the six-days-long pre-climactic activity before the 1951 eruption (which included felt local seismicity, frequent ash-laden explosions of vulcanian type, bulging of the volcano slope accompanied with landslides) was associated with shallow-level intrusion of a highly viscous magma body (cryptodome/dome) of andesitic composition with a volume of approximately 0.01 km3. This intrusion destabilized Mount Lamington's prehistoric intra-crater lava dome.On January 21 the destabilized dome gravitationally collapsed and produced a relatively small-volume debris avalanche, the deposit of which was not recognized during Taylor's original investigation. The debris avalanche had a volume of approximately 0.02–0.04 km3, travelled a distance (L) of 8.5 km and had the ratio of vertical drop (H) to runout (L) of 0.14. The edifice collapse decompressed the intruding cryptodome and triggered its explosive fragmentation.Photographs of the climactic explosion show that the eruptive cloud initially rose vertically but subsequently collapsed upon the terrain around the vent, and formed a PDC which flowed radially outward. The enhanced northward propagation of the PDC to a maximum distance of 13 km reveals that the northern breach in the ancient crater's high walls influenced the distribution of the deposit. In the studied NE-N-NW sector of the devastated area, in the zone proximal to the volcano, the PDC emplaced a normally graded layer of coarse ash and lapilli mixed in the base with picked-up soil and plant fragments. The layer gradually becomes thinner and finer-grained with distance from the volcano. The PDC deposit has a volume of approximately 0.025 km3 and consists of approximately 80% juvenile rock fragments derived from the explosively fragmented cryptodome. The remaining 20% consists of accidental clasts derived from the old volcanic edifice. The juvenile material is crystal-rich andesite with a unimodal vesicularity distribution (4 to 36%). The reconstructed eruption sequence, the PDC tree blowdown pattern and characteristics of the PDC deposit are similar to those of catastrophic laterally-directed blasts of volcanoes Bezymianny in 1956, Mount St.Helens in 1980, and Soufriere Hills, Montserrat in 1997. In contrast to the cases of these “classic” lateral blasts, the blast cloud of Lamington was initially vertically-directed before collapsing to produce a PDC. We speculate that the climactic explosion of Mount Lamington was initially vertical because the rupture surface of the triggering sector collapse intersected the apex of the intruding cryptodome (it exposed a subhorizontal surface of the cryptodome apex), while at Bezymianny, Mount St.Helens, and Soufriere Hills the rupture intersected the main body of the cryptodome/dome, and exposed their steeply inclined surfaces.

Reactivation of an Intraplate Fault by Mine‐Blasting Events: Implications to Regional Seismic Hazard in Western Canada

AbstractMining activities are well known for being able to induce local seismicity but have not yet been shown to cause earthquakes over large distances. We analyze a particular group of seismic events recorded from 2014 to 2016 in north‐central British Columbia (BC) that appear to be triggered by the activities at the Mount Milligan Mine. The spatial distribution of the studied events follows a NW‐SE linear trend, with distances up to approximately 100 km from the mining site. To distinguish mining blasts from blasting‐related and natural events, we adopt a multivariate decision tree based on each event's origin time, distance from the mine, and the pseudo‐spectral acceleration ratios of the three‐component waveforms. The calculated dynamic strains from blasts place a distance limit of 20 km for dynamic triggering. However, accounting for the estimated epicentral uncertainty and temporal distribution of the earthquakes' origin times support the existence of blasting‐triggered events at larger distances (up to ∼50 km) from the mine, suggesting that a previously unmapped fault segment is close to critical state and may have been reactivated. The inferred fault segment aligns remarkably well with the southern extent of the Rocky Mountain Trench and may impose a significant hazard to nearby communities if the entire fault segment of about 150 km‐long ruptures.

Spatial Variations in Crustal and Mantle Anisotropy Across the North American‐Caribbean Boundary on Haiti

AbstractHaiti, on the island of Hispaniola, is situated across the North American‐Caribbean plate boundary at the transition point between oblique subduction in the east and a transform plate boundary in the west. Here we use shear wave splitting measurements from S waves of local (0–50 km) and intermediate depth (50–150 km) earthquakes as well as SK(K)S phases from teleseismic earthquakes to ascertain good spatial and vertical resolution of the azimuthal anisotropic structure. This allows us to place new constraints on the pattern of deformation in the crust and mantle beneath this transitional region. SK(K)S results are dominated by plate boundary parallel (E‐W) fast directions with ~1.9 s delay times, indicating subslab trench parallel mantle flow is continuing westward along the plate boundary. Intermediate depth earthquakes originating within the subducting North American plate show a mean fast polarization direction of 065° and delay time of 0.46 s, subparallel to the relative plate motion between the Caribbean and North American plates (070°). We suggest a basal shear zone within the lower ductile crust and upper lithospheric mantle as being a potential major source of anisotropy above the subducting slab. Upper crustal anisotropy is isolated using shear wave splitting measurements on local seismicity, which show consistent delay times on the order of 0.2 s. The fast polarization directions indicate that the crustal anisotropy is controlled by the fault networks in close proximity to the major strike‐slip faults, which bisect the north and south of Haiti, and by the regional stress field where faulting is less pervasive.

Fulfilling the Information Need After an Earthquake: Statistical Modelling of Citizen Science Seismic Reports for Predicting Earthquake Parameters in Near Realtime

SummaryWhen an earthquake affects an inhabited area, a need for information immediately arises among the population. In general, this need is not immediately fulfilled by official channels which usually release expert-validated information with delays of many minutes. Seismology is among the research fields where citizen science projects succeeded in collecting useful scientific information. More recently, the ubiquity of smartphones is giving the opportunity to involve even more citizens. This paper focuses on seismic intensity reports collected through smartphone applications while an earthquake is occurring. The aim is to provide a framework for predicting and updating in near realtime earthquake parameters that are useful for assessing the effect of the earthquake. This is done by using a multivariate space–time model based on time-varying coefficients and a spatial latent variable. As a case-study, the model is applied to more than 200000 seismic reports globally collected over a period of around 4 years by the Earthquake Network citizen science project. It is shown how the time-varying coefficients are needed to adapt the model to an information content that changes with time, and how the spatial latent variable can capture the local seismicity and the heterogeneity in the people's response across the globe.

Causal mechanism of injection-induced earthquakes through the Mw 5.5 Pohang earthquake case study

Causal mechanisms for fluid injection-induced earthquakes remain a challenge to identify. Past studies largely established spatiotemporal correlations. Here, we propose a multi-process causal mechanism for injection-induced earthquakes through a case study of the 2017 Mw 5.5 induced earthquake near Pohang Enhanced Geothermal System, Korea, where detailed hydraulic stimulation and on-site seismicity monitoring data provide an unprecedented opportunity. Pore pressure modeling reveals that pore pressure changes initiate seismicity on critically stressed faults and Coulomb static stress transfer modeling reveals that earthquake interactions promote continued seismicity, leading to larger events. On the basis of these results, we propose the following causal mechanism for induced seismicity: pore pressure increase and earthquake interactions lead to fault weakening and ultimately triggering larger earthquakes later in the process. We suggest that it is prudent that pore pressure change, initial seismicity locations, and Coulomb static stress transfer from seismicity earlier in the sequence are assessed in real-time.

Return Times of Large Earthquakes Cannot Be Estimated Correctly from Seismicity Rates: 1906 San Francisco and 1717 Alpine Fault Ruptures

AbstractThe unproven assumption that the Gutenberg–Richter (GR) relationship can be extrapolated to estimate the return time, Tr (1/probability of occurrence), of major and large earthquakes has been shown to be incorrect along 196 faults, so far. Here, two more examples of great, well-known faults that do not produce enough earthquakes to fulfill the hypothesis are analyzed. The 300 km section of the San Andreas fault, California, United States, that ruptured in 1906 in the M 8 San Francisco earthquake, produced 200 earthquakes with M≥2 in the last 52 yr, when about 250,000 such events are expected according to the hypothesis. Along a 250 km section that broke in an M 7.9 earthquake in 1717 along the Alpine fault, New Zealand, the number of reported M≥3.6 earthquakes during the last 34 yr was 100, when about 6000 would be expected, based on the hypothesis. Extrapolating the GR relationships for these two fault segments, one estimates Tr of mainshocks of M 8 to be about 10,000 and 100,000 for the 1717 and 1906 ruptures, respectively. Regardless of choice of analysis parameters, this is by factors of 10–400 larger than estimates based on paleogeology, tectonics, and geodesy. In addition, second catalogs for each case yield estimates of probabilities for M 8 earthquakes along the 1717 and 1906 rupture segments that differ by factors of about 2 and 80 (between 5000 and 98,000 yr) from the first respective catalogs. It follows that the probability of large earthquakes cannot be estimated correctly based on local seismicity rates along major faults.

Aftershocks localization and shallow crustal velocity structure following the <italic>M</italic>s6.9 Mainling earthquake in Tibet, China

At 06:34 CST on November 18, 2017, an M s6.9 earthquake struck Mainling prefecture, Nyingchi City, Tibet. The earthquake occurred at the frontier zone of collision and subduction in the eastern Himalayan syntaxis, a region of persistently strong compression between India and Eurasia. To monitor aftershock activity, the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, installed 28 broadband seismic stations around the epicentral area and obtained 180 days of seismic observation data. The average spacing between stations was approximately 5 km, which yielded good coverage of the source area and enriched the seismic data for the Eastern Himalayan syntaxis. In this paper, the hypodense events are refined by the hypoDD double-difference seismic location method and the local tomography software (LOTOS-12), an algorithm for seismic location and velocity structure imaging joint inversion. The hypoDD seismic localization method uses waveform cross-correlation technology to achieve positioning using the minimum residuals of the actual and theoretical travel times of two earthquakes. It is widely used for close-range earthquakes and is suitable for regional earthquake research; the LOTOS algorithm is more appropriate for velocity structure inversion in regions with significant differences in physical properties. The results show that the aftershock zone is approximately 50 km long and 30 km wide and trends NW-SE. According to the aftershock distribution, three active faults are basically consistent with the strike of the Xixingla fault zone. These active fractures are similar in shape and have a NE dip direction, and the dip angles of the active faults gradually become steeper from NW to SE. Under the continuous NE thrusting action of the Namche Barwa syntaxis, the three secondary fractures have undergone bending deformation. This deformation is associated with the adjustment mode of the eastern Himalayan syntaxis where the Indian plate continues to push Eurasia northward. At the same time, combining these results with those of the LOTOS-12 algorithm, the distribution of the Pg wave and Sg wave velocity disturbance in the shallow crust (20 km) and the wave speed ratio ( V p/ V s) are obtained. The main shock was located in an abnormal transition zone of body wave velocity, and the aftershocks mostly occurred in the negative anomaly zone for P wave and S wave velocities, which reflects the characteristics of stratigraphic fractures and faults in the area with concentrated earthquakes. We suggest that this area should be avoided in the future when construction of engineering facilities is required north of Namche Barwa Peak. Overall, with Namche Barwa Peak as the boundary, the P wave and the S wave are generally characterized by high-speed anomalies in the north and low-speed anomalies in the south. This phenomenon may be related to the geological structure and petrophysical properties in this area, as the lithologies of the Lhasa terrane are old and cold; meanwhile, the metamorphic body in the south and the Namche Barwa syntaxis are relatively broken, the ages of rock formation are relatively young, and the lithologies are relatively hot and soft. In addition, high-speed P wave anomalies in the northwestern part of Namche Barwa Peak may be related to enrichment in garnet minerals in this area. The higher wave velocity ratio on the southwest side of the epicentral area, the lower P wave velocity on the right side of profile 1–1′ and the P wave on the left side of profile 2–2′ may be related to the fragmentation of the terrain in this area and the development of valley glaciers. The area where the wave velocity ratio is relatively large may also be related to the upwelling of asthenospheric and lithospheric material in the deep mantle.

Ongoing research on the pumping-induced land deformation in the Aguascalientes Valley: an analysis of the recent data of vertical deformation, groundwater level variations and local seismicity

Abstract. In the Aguascalientes valley, middle Mexico, the demand of groundwater from the local aquifer system was suddenly increased after the late 1970s. Since then, several related problems have been occurring or become critical such as land subsidence, ground fissuring, and low-magnitude earthquakes. The most recent data of vertical deformation from PSInSAR, groundwater levels, and earthquakes, has provided critical information regarding the relationship amongst all these processes. In particular, that related to land subsidence, earth fissuring and seismicity. Regarding this, more satellite imagery and data from GPS stations are being revised as a possibility of a more generalized vertical deformation derived with low-magnitude seismicity. A particular seismic event recorded on 6 April 2019 has revealed critical information on the close association between vertical displacements occurred in active faults and low-magnitude seismic events.

Tsunami intensity scale based on wave amplitude and current applied to the French Riviera: the case study of local seismicity

The French–Italian Riviera faces several geophysical hazards, including recurrent earthquakes and underwater landslides that can be tsunamigenic. The stakes are high since this is a densely populated and touristic area. Several studies have already been carried out, in particular to map tsunami hazard resulting from the near-field seismicity of the North Ligurian Faults System, which is located a short distance off the coast. In our most recent study, runup maps were developed together with local analyses of tsunami-induced current fields. However, no conclusions were drawn, based on these results, as of the associated tsunami risk along the coast. Here, to this effect, we apply a recently proposed tsunami intensity scale to the simulation results obtained in our previous work (maximum values of tsunami depths and currents). This intensity scale (7 levels) is mapped over the entire coastal area, and its site-specific values are discussed. The scale allows quantifying the potential damage inland and at sea, based on a standard coastal vulnerability that has been assessed through different records. It thus represents a useful tool to help improving our preparedness to tsunami hazard.

Antinoise performance of time-reverse imaging conditions for microseismic location

A suitable imaging condition is critical for the success of seismic imaging or source location. To understand what imaging condition to select for handling noisy data, the antinoise performance of the maximum amplitude imaging condition (MAIC), the autocorrelation imaging condition (ACIC), and the geometric mean imaging condition (GMIC) were comparatively studied. Synthetic microseismic data based on the Marmousi2 model, with different levels of synthetic Gaussian noise and field noise separately added, were used for tests. For Gaussian noise data, five signal-to-noise (S/N) ratio levels were considered, ranging from an absolutely clean level of [Formula: see text] to an extremely noisy level of [Formula: see text], in an increment of five times of the lower level of S/N. It was found that the antinoise ability of MAIC outperforms ACIC, and ACIC outperforms GMIC. This conclusion was confirmed to be valid for field noise in the further experiments performed, using 16 groups of industrial noise recordings from different areas. The statistical analysis shows these performance differences are statistically consistently significant. In terms of spatial resolution, it is the other way around; that is, GMIC outperforms ACIC, and ACIC outperforms MAIC. These suggest that in choosing a suitable imaging condition for time-reverse imaging location, one needs to consider the balance between the resolution demand and data quality requirement. If the data quality is very high, GMIC may be used to achieve a high-resolution location result. Conversely, if the data quality is poor, MAIC is a good choice for obtaining a robust location result. In between, ACIC or grouped GMIC is a proper approach to work out a balanced result for resolution demand and the noisy level provision.

Seismogenic thickness of California: Implications for thermal structure and seismic hazard

The seismogenic thickness of the crust, a proxy for brittle-crust thickness, is a geometric parameter related to crustal strength, seismic hazard, and the crust's thermo-mechanical nature. We use high-resolution earthquake-location data from California to construct a topographic map of the base of the seismogenic crust by calculating the depth above which 95% of seismicity (D95) is located for fixed width bins. Seismogenic thickness is highly variable, ranging from ~5 km to >30 km, with thicker D95 values in the Great Valley-Sierra Nevada and thinner values in the Walker Lane and northern coastal California. Seismogenic thickness is inversely correlated with surface heat flow in most locations, consistent with a steady-state conductive crust, and local deviations probably reflect non-steady-state conditions related to magmatism and/or hydrothermal circulation. Such correlation suggests that, at regional scale, brittle-ductile transition (BDT) depth is mostly controlled by geothermal gradients, and the base of the seismogenic crust essentially represents a BDT isotherm (~300–350 °C for quartz-dominated lithologies). Spatial variations of D95 depths across California can be used to evaluate or constrain the locations of future seismicity, propagation direction of earthquake ruptures, and maximum depth, rupture area, and magnitude of future strike-slip earthquake events. Thicker seismogenic crust has a greater integrated strength. Seismogenic depth asperities, which represent mechanically stronger crustal patches, may focus and nucleate future earthquake events and/or impede rupture propagation.

Upper Mantle Structure of the Southern U.S. Continental Margin From Teleseismic Traveltime Tomography

AbstractThe southern U.S. continental margin records a rich tectonic history spanning ~1.35 Ga, including two complete Wilson cycles. Due to a thick sediment cover, the paucity of local seismicity, and sparse seismic instrumentation, the tectonomagmatic evolution of this passive margin remains uncertain. The recent USArray seismic network offers an opportunity to address unresolved issues by imaging the crust and upper mantle. Direct teleseismic P and S traveltimes recorded at ~1,600 stations are mapped into 3‐D velocity perturbations. P and S tomography models, although generated independently, are broadly consistent, with a strong correlation between anomaly patterns in the sublithospheric mantle and known crustal features. Fast mantle velocities correspond to the Laurentia Craton and Llano and Grenville terranes, while intracratonic rift systems and Paleozoic arc terranes are marked by slow anomalies in the upper mantle.

Geodynamic subduction models constrained by deep earthquakes beneath the Japan Sea and eastern China

Details of Pacific plate subduction under the Japan Sea and associated current seismicity remain challenging. Seismic tomography reveals a continuous slab dipping at ~30° down to ~600 km, and earthquake mechanisms point to down-dip compression. Further, the slab is lying at the 660-km discontinuity, and this zone is aseismic. We suggest that this pattern results from the slab’s negative thermal buoyancy, resistance of the viscous lower mantle, and buoyancy forces associated with the phase transitions at 410 km and 660 km. Our model comprises an ageing subducting plate, nonlinear rheology and major phase transitions. The model explains the observed low dip angle of the slab and predicts a detailed stress pattern related to bending down to 450 km, followed by unbending as the slab is laid flat upon the 660 km boundary. Remarkably, in the bending/unbending regions, down-dip compression occurs close to the slab top/bottom, respectively. As only down-dip compression is observed, we argue that the earthquakes are mapping the top and bottom of the slab. The absence of seismicity in the flat-lying slab is explained by significantly lower stresses and higher temperatures. With this new knowledge, increasingly accurate seismic locations will considerably improve images of finite-extent slab geometry.

Subsidence associated with oil extraction, measured from time series analysis of Sentinel-1 data: case study of the Patos-Marinza oil field, Albania

Abstract. The Patos-Marinza oil field in central Albania (40.71∘ N, 19.61∘ E), operated since 1939, is one of the largest onshore oil fields in Europe. More than 7 million oil barrels are extracted every year from the Messinian sandstone formations of the Durres Basin in the Albanian Peri-Adriatic Depression by the Bankers Petroleum Ltd. (hereafter Bankers), which has been operating the field since 2004. In this study, we take advantage of the new Sentinel-1 radar images acquired every 6 to 12 d over Albania to measure the surface displacement in the Myzeqeja plain and in the Patos-Marinza oil field in particular. Images from two ascending and descending tracks covering the area are processed through a radar interferometry (InSAR) time series analysis over the 2014 to 2018 time span, providing consistent average line-of-sight (LOS) velocity maps and displacement time series. The regional deformation field exhibits a slow subsidence of the entire basin relative to the highlands (at rates of 2.5 mm yr−1) that we interpret as a combination of natural and human-induced compaction. This broad picture is complicated by a very strong local subsidence signal with rates as high as 15 mm yr−1 that spatially correlates with the Patos-Marinza oil field and is maximal in the zone holding most of the operating wells, where enhanced oil recovery techniques are used. The striking spatial correlation between the maximum subsidence area and the active wells, as seen from optical images, argues in favor of surface deformation induced by oil extraction. This deformation is well reproduced by elastic models mimicking the basin and reservoir compaction using planar negative tensile (closing) dislocations. Such modeling provides a first-order estimation of the volumetric deflation rate in the oil reservoir (∼0.2 Mm3 yr−1), and it suggests that concurrent injection activity has been conducted in the central part of the field where small uplift is observed. Our new InSAR-derived evidence of significant surface strain associated with the oil field operations raises the question of the potential impact of these operations on the local seismicity. A slight increase in the nearby released seismic moment rate seems to be observed since 2009, shortly after the oil field reactivation. However, without further seismological monitoring of the area and longer InSAR time series, this question will remain open.

Comparison of fully non-stationary artificial accelerogram generation methods in reproducing seismicity at a given site

Seismic input modelling is a crucial step when Non-Linear Time-History Analyses (NLTHAs) are performed, the seismic response of structures being highly responsive to the input employed. When natural accelerograms able to represent local seismicity are not available, the use of generated accelerograms is an efficient solution for input modelling. The aim of the present paper is to compare four methods for generating fully non-stationary artificial accelerograms on the basis of a target spectrum, identified using seven recorded accelerograms registered in the neighbourhood of the construction site during a single event, assumed as target accelerograms. For each method, seven accelerograms are generated and used to carry out NLTHAs on three RC structures, having irregular mass and stiffness distributions. The generation methods are evaluated in terms of both input modelling and seismic response of three RC structures. The results point out that maximum interstorey drift ratios are well reproduced only by generation methods based on spectrum-compatible criterion, while energy contained by the target set is only simulated by methods based on records of natural signals. Moreover, none of the method here investigated is able to reproduce the hysteretic energy dissipated by the structures subjected to the target accelerograms, in terms of both total amount and cumulative trend over the duration.

Moment Capacity Ratio at Column – Beam Joint in a RC Framed Structure

Beam-column joint is the gap in the modern ductile design of building. Especially under the earthquake loading this is more susceptible to damage. Due to brittle nature of failure this type of failure cannot be afford. Since 1970’s this areas is under the light of research, but with the paper of Park and Paul, It got momentum. But still due to versatile nature of the joints core behaviour, the problem is still persisting. Though many international codes recommend the moment capacity ratio at beam column joint to be more than one, There are discrepancies among the major international codes with regard to MCR. Indian standard codes for design of RC framed buildings are silent on this aspect. Draft 13920 (2014) code suggests a value of MCR similar to other international codes without proper theoretical basis. Hence a rational study is required on the values of MCR. A computationally attractive procedure for calculating flexural capacity of column developed for determining MCR at a beam-column joint. To reach at an appropriate and acceptable MCR for capacity design of RC framed building reliability based approach is done. This research deals with the fragility and reliability analysis of five, seven and ten storey RC frames designed using various values of MCR ranging from 1.0 to 3.2. The RC frames are designed as per IS 1893 (2002) for all seismic zones. Hazard curves required of various seismic location in India (like zone II, III, IV and V) has been selected from National Disaster Management Authority, Government of India. Seismic risk assessment of all the designed buildings is conducted and based on the achieved Reliability Index and the Target Reliability Index minimum value of Moment Capacity Ratio (MCR) is suggested.

Seasonal patterns of 3D crustal motions across the seismically active southeastern Tibetan Plateau

We study the three-dimensional (3D) seasonal crustal deformation and its relationship with local seismicity based on continuous GPS (cGPS), mass loading models and seismicity data covering the period from 2010 to 2018 in the southeastern Tibetan Plateau (SETP). Of the 3D seasonal motions, vertical motion is the most significant, followed by the northward and eastward directions, with average annual amplitudes from cGPS of 9.28 mm, 1.62 mm and 0.72 mm, respectively. The annual motions predicted by the hydrological mass loading (HYDL) model in all directions are about 3–4 times larger than that of the atmospheric mass loading (ATML) model, but smaller than the cGPS measurements. The initial phase difference between the cGPS and loading models can be nearly eliminated by combining the ATML and HYDL models which helps to fit the cGPS results better. The average weighted root-mean-square (WRMS) reduction ratios of the ATML, HYDL model and their combination are 0.30, 0.77 and 0.88, respectively. This indicates that the seasonal vertical crustal motions observed by cGPS in the SETP are dominated by seasonal loading motions from the ATML and HYDL. In four subregions where no M > 4 earthquakes had occurred in the past decade, we observe an anti-correlation between equivalent water height (EWH) from the GRACE (Gravity Recovery and Climate Experiment) and the vertical displacement derived by cGPS. It shows an anti-correlation relationship between the EWH and seismicity in three subregions and positive correlation in one subregion, which underscores the importance of hydrological loading on seismicity in the SETP.

Earthquake detection in the Jiangsu region, China using graphics-processing-unit-based Match & Locate and rapid earthquake association and location*

Earthquake detection and location are essential in earthquake studies, which generally consists of two main classes: waveform-based and pick-based methods. To evaluate the ability of two different methods, a graphics-processing-unit-based Match & Locate (GPU-M&L) method and a rapid earthquake association and location (REAL) method are applied to continuous seismic data recorded by 24 digital seismic stations from Jiangsu Seismic Network during 2013 for comparison. GPU-M&L is one of waveform-based methods by waveform cross-correlations while REAL is one of pick-based method to associate arrivals of different seismic phases and locate events through counting the number of P and S picks and travel time residuals. Twenty-six templates are selected from the Jiangsu Seismic Network local catalog by using the GPU-M&L. The number of newly detected and located events is about 2.8 times more than those listed in the local catalog. We both utilize a deep-neural-network-based arrival-time picking method called PhaseNet and a short-term/long-term average (STA/LTA) trigger algorithm for seismic phase detection and picking by applying the REAL. We then refine seismic locations using a least-squares location method (VELEST) and a high-precision relative location method (hypoDD). By applying STA/LTA and PhaseNet, 1006 and 1893 events are associated and located, respectively. The newly detected events are mainly clustered and show steeply dipping fault planes. By analyzing the performance of these methods based on long-term continuous seismic data, the detected catalogs by the GPU-M&L and REAL show that the magnitudes of completeness are 1.4 and 0.8, respectively, which are smaller than 2.6 given by the local catalog. Although REAL provides improvement compared with GPU-M&L, REAL is highly dependent on phase detection and picking which is strongly affected by signal-noise ratio (SNR). Stations at southeast of the study region with low SNR may lead to few detections in the same area.

Earthquake-induced loss assessment of steel buildings designed to Eurocode 8

The main objective of this paper is to understand and characterize the level of expected earthquake-induced economic losses of steel buildings designed to Eurocode 8. This is attained through the use of a comprehensive population of case-study buildings that considers different lateral load resisting systems, plan configurations and building heights. Different locations of low and high seismicity, reflecting the majority of the European seismic reality, are considered. The results indicate that EC8-compliant steel moment-resisting frame (MRF) buildings and concentrically-braced frame (CBF) buildings generally exhibit good seismic performance in terms of mean annual frequency of reaching collapse. Although all buildings showed good performance against collapse, when compared to the requirements present in literature, clear indications on a lower performance of chevron-braced CBFs are observed. Furthermore, low expected annual losses (EALs) are recorded across the population of steel buildings considered, with a predominant contribution of losses coming from structural and non-structural damage. Based on the findings reported in this paper, different insights towards the incorporation of loss performance objectives in the European seismic design code are provided.