How Fault Surface Features Can Tell Us About Future Earthquakes

A new study suggests ways to quantify fault maturity, a property that affects earthquake characteristics.

Large slip, long duration, and moderate shaking of the Nicaragua 1992 tsunami earthquake caused by low near-trench rock rigidity

Large earthquake ruptures propagating up to areas close to subduction trenches are infrequent, but when they occur, they heavily displace the ocean seafloor originating destructive tsunamis. The current paradigm is that the large seafloor deformation is caused by local factors reducing friction and increasing megathrust fault slip, or prompting the activation of ancillary faults or energy sources. As alternative to site-specific models, it has been proposed that large shallow slip could result from depth-dependent rock rigidity variations. To confront both hypotheses, here, we map elastic rock properties across the rupture zone of the MS7.0-MW7.7 1992 Nicaragua tsunami earthquake to estimate a property-compatible finite fault solution. The obtained self-consistent model accounts for trenchward increasing slip, constrains stress drop, and explains key tsunami earthquake characteristics such as long duration, high-frequency depletion, and magnitude discrepancy. The confirmation that these characteristics are all intrinsic attributes of shallow rupture opens new possibilities to improve tsunami hazard assessment.

Effects of Earthquake Magnitude, Distance, and Site Conditions on Spectral and Pseudospectral Velocity Relationship

ABSTRACT The spectral velocity (SV) is necessary information in the seismic design of structures with supplemental velocity-dependent dampers, and it is conventionally approximated by the pseudospectral velocity (PSV), which is available in seismic codes. Because of the significant approximation error, it is important to clarify the relationship between the two spectra to establish a suitable formulation to relate SV to PSV. Recent studies have point out that this relationship is influenced not only by the oscillator period and damping ratio but also by earthquake characteristics (Papagiannopoulos et al., 2013; Samdaria and Gupta, 2018). To clarify the seismological effects, in this study, an approach to relate SV to PSV based on the random vibration theory is proposed, and it is verified by comparing its results with those of traditional time-series analysis. The effects of earthquake magnitude and distance as well as site conditions on the relationship between the two spectra are explored based on the proposed approach as well as statistical analysis of recorded seismic motions. It is found that the SV approaches the PSV with increasing magnitudes at long oscillator periods but performs oppositely at short oscillator periods. The demarcation range beyond which the opposite trend is observed varies from (0.07–0.24) to (0.12–0.87) s using the proposed approach and considering the regions of central and eastern North America. The range varies from (0.1–0.15) to (0.3–0.7) s based on the results obtained by the statistical analysis of seismic records in Japan. The observed phenomena were theoretically explained, and the seismological effects were found to be governed by the ground-motion frequency content.

Penentuan Karakteristik Mekanisme Gempa Tahun 2018-2019 Di Nusa Tenggara Menggunakan Metode Inversi Momen Tensor

Nusa Tenggara is one of the areas with a high level of seismic activity in Indonesia because this area is located between the Indian Ocean plate, which moves northward and pushes the Eurasian plate. One method that is often used to determine an earthquake's epicentre is the Tensor Moment Inversion method. This study aims to determine the moment tensor magnitude of each earthquake event and determine earthquake characteristics based on the earthquake focus mechanism in Nusa Tenggara from 2018 to 2019. The earthquake with a magnitude of ≥ 5.7 SR and to find out the fault parameters, namely strike, dip, and rake using waveform data. One method that is often used to determine an earthquake's epicentre is the Tensor Moment Inversion method. The results showed that the fault planes formed were reverse faults and oblique faults. It has been calculated the moment tensor for each of the six components, namely Mxx, Myy, Mzz, Mxy, Myz and Mxz. From the results of the focal analysis of the 2018-2019 Nusa Tenggara earthquake mechanism, the values of the fault plane orientation parameters such as strike, dip and rake are obtained. For strikes in Nusa Tenggara on area 1, namely: 73° to 122°, Dip: 20° to 72° and Rake: 53° to 139°. While in field 2 for a strike, it is 232° to 280°, Dip 28° to 75°, Rake: 52° to 102°.

Seismic analysis of the rail-counterweight system in elevators considering the stiffness of rail brackets

The rail in the rail-counterweight system in elevators is vertically supported along the building height by the rail brackets. In the numerical model of the rail-counterweight system, the rail-bracket assembly is modelled as a continuous beam supported by linear springs representing the rail brackets and the stiffness of the bracket is contributed to the overall stiffness of the rail-bracket assembly. To investigate the effect of the rail brackets on the seismic responses of the rail-counterweight system, a parameter named “stiffness ratio” is proposed in a rail-bracket assembly, defined as the ratio of the stiffness of the bracket to that of the simply supported continuous beam representing the rail at mid-span of an intermediate span. The stiffness of the brackets is varied by changing the stiffness ratio of the rail-bracket assembly, and the corresponding seismic responses of the rail-counterweight system are analyzed, including the maximum stress in the rail, the maximum deformation of the brackets, and the maximum displacement of the roller guide off the rail. A comprehensive analysis is conducted by considering four rail spans and three earthquake motions. The variations of the responses with the increasing stiffness ratio are dependent on the earthquake characteristics and the rail spans. The less the rail span is, the less important the effects of the stiffness ratio are. Nevertheless, the seismic responses of the rail-counterweight system generally have little change when the stiffness ratio is up to 4 and more. It is indicated that increasing of the stiffness ratio are not necessarily capable of improving the seismic performance of the counterweight system, especially when the stiffness ratio or the stiffness coefficient of the brackets is large, varying the stiffness ratio is unhelpful to change the rail-counterweight responses.

Linked 3-D modelling of megathrust earthquake-tsunami events: from subduction to tsunami run up

SUMMARY How does megathrust earthquake rupture govern tsunami behaviour? Recent modelling advances permit evaluation of the influence of 3-D earthquake dynamics on tsunami genesis, propagation, and coastal inundation. Here, we present and explore a virtual laboratory in which the tsunami source arises from 3-D coseismic seafloor displacements generated by a dynamic earthquake rupture model. This is achieved by linking open-source earthquake and tsunami computational models that follow discontinuous Galerkin schemes and are facilitated by highly optimized parallel algorithms and software. We present three scenarios demonstrating the flexibility and capabilities of linked modelling. In the first two scenarios, we use a dynamic earthquake source including time-dependent spontaneous failure along a 3-D planar fault surrounded by homogeneous rock and depth-dependent, near-lithostatic stresses. We investigate how slip to the trench influences tsunami behaviour by simulating one blind and one surface-breaching rupture. The blind rupture scenario exhibits distinct earthquake characteristics (lower slip, shorter rupture duration, lower stress drop, lower rupture speed), but the tsunami is similar to that from the surface-breaching rupture in run-up and length of impacted coastline. The higher tsunami-generating efficiency of the blind rupture may explain how there are differences in earthquake characteristics between the scenarios, but similarities in tsunami inundation patterns. However, the lower seafloor displacements in the blind rupture result in a smaller displaced volume of water leading to a narrower inundation corridor inland from the coast and a 15 per cent smaller inundation area overall. In the third scenario, the 3-D earthquake model is initialized using a seismo-thermo-mechanical geodynamic model simulating both subduction dynamics and seismic cycles. This ensures that the curved fault geometry, heterogeneous stresses and strength and material structure are consistent with each other and with millions of years of modelled deformation in the subduction channel. These conditions lead to a realistic rupture in terms of velocity and stress drop that is blind, but efficiently generates a tsunami. In all scenarios, comparison with the tsunamis sourced by the time-dependent seafloor displacements, using only the time-independent displacements alters tsunami temporal behaviour, resulting in later tsunami arrival at the coast, but faster coastal inundation. In the scenarios with the surface-breaching and subduction-initialized earthquakes, using the time-independent displacements also overpredicts run-up. In the future, the here presented scenarios may be useful for comparison of alternative dynamic earthquake-tsunami modelling approaches or linking choices, and can be readily developed into more complex applications to study how earthquake source dynamics influence tsunami genesis, propagation and inundation.

A suite of ground motion prediction equations for cumulative absolute velocity in shallow crustal earthquakes including epistemic uncertainty

Recent research has highlighted the usefulness of cumulative absolute velocity [Formula: see text] in several contexts, including using the [Formula: see text] at the ground surface for earthquake early warning and using the [Formula: see text] at rock reference conditions for evaluation of the liquefaction risk facing structures. However, there are relatively few ground motion prediction equations for CAV, they are based on relatively small data sets, and they give relatively similar results. This study develops nine ground motion prediction equations for [Formula: see text] based on a global database of ground motion records from shallow crustal earthquakes. Its provision of nine models enables characterization of epistemic uncertainty for ranges of earthquake characteristics that are sparsely populated in the regression database. The functional forms provide different perspectives on extrapolation to important ranges of earthquake characteristics, particularly large magnitude events and short distances. The variability and epistemic uncertainty in the models are characterized. Spatial autocorrelation of the models’ errors is investigated. The models’ predictions agree with existing broadly applicable models at small to moderate magnitudes and moderate to long distances. These models can be used to improve hazard analysis of [Formula: see text] that incorporates the influence of epistemic uncertainty.

Establishment of Artificial Accelerogram for Structural Analysis according to the Earthquake Characteristics of Vietnam

This paper presents the method of establishing artificial accelerogram for analysis and calculation of structures in accordance with seismic characteristics and earthquake risk in one specific construction areas in Vietnam. The artificial accelerogram allow to analyze nonlinear or linear dynamic behavior of the structures in time series in accordance with Vietnam National Standards for Design of structures for earthquake resistances (TCVN 9386: 2012) and seismic parameters specified in Vietnam Building Code on Natural Physical and Climatic Data for Construction (QCVN 02:2009-BXD). The accelerograms are also used as input parameters for shaking table tests by Vietnam's most modern sharking table at the Vietnam Institute for Building Science and Technology.