Using LSTM Neural Networks for Onsite Earthquake Early Warning

Onsite earthquake early warning (EEW) systems determine possible destructive S waves solely from initial P waves and issue alarms before heavy shaking begins. Onsite EEW plays a crucial role in filling in the blank of the blind zone near the epicenter, which often suffers the most from disastrous ground shaking. Previous studies suggest that the peak P-wave displacement amplitude (Pd) may serve as a possible indicator of destructive earthquakes. However, the attempt to use a single indicator with fixed thresholds suffers from inevitable errors because the diversity in travel paths and site effects for different stations introduces complex nonlinearities. In addition, the short warning time poses a threat to the validity of EEW. To conquer the aforementioned problems, this study presents a deep learning approach employing long short-term memory (LSTM) neural networks, which can produce a highly nonlinear neural network and derive an alert probability at every time step. The proposed LSTM neural network is then tested with two major earthquake events and one moderate earthquake event that occurred recently in Taiwan, yielding the results of a missed alarm rate of 0% and a false alarm rate of 2.01%. This study demonstrates promising outcomes in both missed alarms and false alarms reduction. Moreover, the proposed model provides an adequate warning time for emergency response.

A morpho-tectonic approach to the study of earthquakes in Rome

Rome has the world’s longest historical record of felt earthquakes, with more than 100 events during the last 2,600 years. However, no destructive earthquake has been reported in the sources and all of the greatest damage suffered in the past has been attributed to far-field events. While this fact suggests that a moderate seismotectonic regime characterizes the Rome area, no study has provided a comprehensive explanation for the lack of strong earthquakes in the region. Through the analysis of the focal mechanism and the morphostructural setting of the epicentral area of a "typical" moderate earthquake (ML = 3.3) that recently occurred in the northern urban area of Rome, we demonstrate that this event reactivated a buried segment of an ancient fault generated under both a different and a stronger tectonic regime than that which is presently active. We also show that the evident structural control over the drainage network in this area reflects an extreme degree of fragmentation of a set of buried faults generated under two competing stress fields throughout the Pleistocene. Small faults and a present-day weaker tectonic regime with respect to that acting during the Pleistocene explain the lack of strong seismicity and imply that a large earthquake could not reasonably occur.

Numerical Performance of Energy Dissipation Slotted Plate for Bridge Unseating Prevention

Recently, the bridge unseating prevention devices are widely used in active seismic zones. These devices are stiffness dependant, velocity dependant and energy dissipation devices. The energy dissipation devices are designed to overcome the energy that transfers from bridge substructure to superstructure. However, the current devices are not controlled to function with different ground motion intensities and should be replaced after yielding. Therefore, this research introduced a slotted plate energy dissipation device with three parts, each part function in known deformation range. The slotted plate behavior has been evaluated numerically by finite element method. Displacement control and load control analysis has been done, and then the effect of steel grade is studied to predict the suitable steel properties for designing the plate. Moreover, the slotted plate behavior is applied in 3D bridge seismic analysis to assess the multi-level performance and the ability to overcome the seismic effect on the bridge in longitudinal direction. The results approved the capability of the plate to dissipate energy in multi-stage of deformation. The lower steel grade is suitable for low to moderate earthquake zone and the high grade can be used in severe ground motion areas. Furthermore, the bridge longitudinal behavior has enhanced with different steel grades of the slotted plate.

Slow build-up of turbidity currents triggered by a moderate earthquake in the Sea of Marmara

Earthquake-induced submarine slope destabilization is known to cause debris flows and turbidity currents, but the hydrodynamic processes associated with these events remain poorly understood. Records are scarce and this notably limits our ability to interpret marine paleoseismological sedimentary records. An instrumented frame comprising a pressure recorder and a Doppler recording current meter deployed at the seafloor in the Sea of Marmara Central Basin recorded consequences of a MW = 5.8 earthquake occurring Sept 26, 2019 and of a Mw = 4.7 foreshock two days before. The smaller event caused sediment resuspension but no strong current. The larger event triggered a complex response involving a mud flow and turbidity currents with variable velocities and orientations, which may result from multiple slope failures. A long delay of 10 hours is observed between the earthquake and the passing of the strongest turbidity current. The distance travelled by the sediment particles during the event is estimated to several kilometres, which could account for a local deposit on a sediment fan at the outlet of a canyon, but not for the covering of the whole basin floor. We show that after a moderate earthquake, delayed turbidity current initiation may occur, possibly by ignition of a cloud of resuspended sediment. Some caution is thus required when tying seismoturbidites with earthquakes of historical importance. However, the horizontal extent of the deposits should remain indicative of the size of the earthquake.

Sensitivity of Earthquake Damage Estimation to the Input Data (Soil Characterization Maps and Building Exposure): Case Study in the Luchon Valley, France

This article studies the effects of the soil data and exposure data of residential building inventories, as well as their spatial resolution, on seismic damage and loss estimates for a given earthquake scenario. Our aim is to investigate how beneficial it would be to acquire higher resolution inventories at the cost of additional effort and resources. Seismic damage computations are used to evaluate the relative influence of varying spatial resolution on a given damage model, where other parameters were held constant. We use soil characterization maps and building exposure inventories, provided at different scales from different sources: the European database, a national dataset at the municipality scale, and local field investigations. Soil characteristics are used to evaluate site effects and to assign amplification factors to the strong motion applied to the exposed areas. Exposure datasets are used to assign vulnerability indices to sets of buildings, from which a damage distribution is produced (based on the applied seismic intensity). The different spatial resolutions are benchmarked in a case-study area which is subject to moderate-to-average seismicity levels (Luchon valley in the Pyrénées, France). It was found that the proportion of heavily damaged buildings is underestimated when using the European soil map and the European building database, while the more refined databases (national/regional vs. local maps) result in similar estimates for moderate earthquake scenarios. Finally, we highlight the importance of pooling open access data from different sources, but caution the challenges of combining different datasets, especially depending on the type of application that is pursued (e.g., for risk mitigation or rapid response tools).

ASSESSMENT OF PRECAST WIDE U BEAM-COLUMN SYSTEM FOR MITIGATION OF STRUCTURAL FAILURE FROM SEISMIC HAZARD IN THAILAND

A large number of low to moderate earthquake incidents have been witnessed in the northern and western parts of Thailand. These incidents usually lead to various damage levels in various structures. Therefore, a sufficient lateral force resisting structures should be designed for the construction in such earthquake-prone areas. This paper presents the relevance of using a typical composite wide U beam-column system for mitigation of structural failure and collapse from the seismic hazard in Thailand. The investigated composite structural system consists of precast U beams, precast columns, and cast-in-situ concrete over the precast U beams and in the joint regions. The system also includes post-tensioning in the cast-in-situ area of the composite beams. The system has widely been used in low- to mid-rise commercial building in Thailand. In order to scrutinize the seismic performance of the system, a half-scale specimen of the post-tensioned precast U beam-column joint was tested under an incremental displacement-controlled lateral cyclic load. The laboratory test revealed the drift capacity, damage pattern, strain development in the rebars etc. of the precast wide U beam-column interior joint. Based on the obtained drift capacity, displacement-based assessment of the system was carried out. In addition, the observed damages on the tested structure were evaluated using damage grading criteria for building subjected to earthquake. The assessment showed a high potential of the post-tensioned precast wide U beam-column system to mitigate the structural failure and collapse from the earthquake hazard. However, some improvements in the current seismic performance of the system are required to employ the system in high seismic zones.

Influence of Maxwell Stiffness in Damage Control and Analysis of Structures with Added Viscous Dampers

Viscous damping systems are often implemented in structures to reduce seismic damage. The stiffness of these elements is dominated by the most flexible part of the set including brace extender, auxiliary mounting elements and damping unit. Existing experimental data are used in this study to show that the actual stiffness of the set is about 25% to 50% of the value generally adopted in current engineering practice, which is based solely on the brace extender. A numerical study shows that this reduction has large implications for several variables related to damage control: residual drift ratio, storey acceleration and plastic strain energy dissipated by the frame members. Other variables, such as member forces and rotations, can experience large variations, particularly for non-linear dampers and high damping levels, especially in the top part of the building and more conspicuously for moderate earthquake intensities. In the absence of accurate data, Maxwell stiffness for analysis based on brace extender properties should be substantially reduced, with recommended factors between 0.25 and 0.50. Given the scarcity of experimental data, these results should be considered preliminary.

A decade of seismicity in metropolitan France (2010-2019): the CEA/LDG methodologies and observations

We summarize ten years of the French seismicity recorded by the Geophysical and Detection Laboratory (LDG) of the French Alternative Energies and Atomic Energy Commission (CEA) network from 2010 to 2019. During this period, 25,279 natural earthquakes were detected by the LDG and located within metropolitan France and its immediate vicinity. This seismicity contributes to more than 47% of the natural earthquakes instrumentally recorded since 1962 (mainly due to the improvement of network capacity), and includes about 28% of the most significant earthquakes with a magnitude ML ≥ 4.0. Recent seismic events therefore significantly expand the available national catalogues. The spatial distribution of 2010-2019 earthquakes is broadly similar to the previous instrumental pattern of the seismicity, with most of the seismic activity concentrated in the French Alps, the Pyrenees, the Brittany, the upper Rhine Graben and the Central Massif. A large part of the seismic activity is related to the occurrence of individual events. The largest earthquakes of the last ten years include the November 11, 2019 Le Teil earthquake with ML 5.4 and maximal epicentral intensities VII to VIII, which occurred in the Rhone valley; the April 28, 2016 La Rochelle earthquake with ML 5.2 and epicentral intensity V, which occurred at the southernmost extremity of the Armorican Massif in the vicinity of the Oléron island; and the April 7, 2014 Barcelonnette earthquake with ML 5.1 and epicentral intensity VII, which occurred in the Ubaye valley in the Alps. In 2019, two other moderate earthquakes of ML 5.1 and ML 4.9 stroke the western part of France, in Charente-Maritime and Maine-et-Loire department, respectively. The recent moderate earthquake occurrences and the large number of small earthquakes recorded give both the potential to revise some regional historical events and to determine more robust frequency-magnitude distributions, which are critical for seismic hazard assessment but complex due to low seismicity rates in France. The LDG seismic network installed since the early 1960s also allows a better characterization of the temporal structure of seismicity, partly diffused and in the form of mainshock-aftershocks sequences or transient swarms. These aspects are important in order to lower the uncertainties associated to seismogenic sources and improve the models in seismic hazard assessment for metropolitan France.

Structural reconstruction, fault parameterization, and slip rate analysis in the northern Adriatic Sea (Italy): implications for the Plio-Pleistocene tectonic activity of long-lived offshore buried thrusts.

<p>The northern Apennines foredeep is characterized by a Plio-Pleistocene tectonic activity whose driving structures (thrust faults and related anticlines) are always buried by a high amount of syntectonic sediments, both onshore (Po Plain) and offshore (Adriatic Sea), thereby leaving subtle or none apparent signatures in the topo-bathymetry. Compared to the rest of Italy, this area has a relatively moderate earthquake hazard, but historical reports and instrumental recordings testify for significant seismicity. Seismological analyses of recent sizeable earthquakes (e.g., the Mw 6.1, Emilia earthquake in 2012) confirmed that the seismic activity is mainly due to the outermost northern Apennines buried thrusts. In this work, we reconstructed and parameterized the 3D geometry of such buried faults in an offshore sector just south of the Po River delta by interpreting a dense network of 2D seismic reflection profiles. The availability of two regional seismic reflection profiles, coupled with a detailed reconstruction of Plio-Pleistocene horizons, allowed us to restore the deformation cumulated by these thrusts. Our analysis was aimed at (1) establishing the age of inception of the main crustal thrusts, (2) reconstruct the main Plio-Pleistocene tectonic events affecting the study area, and (3) calculate the Plio-Pleistocene slip rates at different time slices and reporting them through probability distribution functions that take into account the uncertainties associated with horizon ages and restoration parameters. Our results show that the Plio-Pleistocene tectonic activity is variably distributed on different thrust faults and decreases exponentially over time after the Gelasian. The analysis performed on the most recent reflectors suggests that a low but not negligible tectonic activity characterizes the main thrusts in the studied region in the last 4-500 ka and hints at a residual activity that may last until the present.</p>