Multisource Ground Motion Attenuation Relationship Model for the Vertical Component of the Wenchuan Earthquake on May 12, 2008

In order to extend the multisource model to vertical ground motion, we fit the vertical ground motion attenuation relationship of the Wenchuan earthquake. Different from traditional attenuation relationship forms, we propose a simplified ground motion attenuation function including site effect via a flag related to VS30. The regression results show that it has site effect on the vertical ground motion of the Wenchuan earthquake and gradually weakens with the increase in periods. According to residuals analysis, the hanging-wall effect on vertical ground motion is strong for the Wenchuan earthquake, especially in short periods. The result analysis indicates that the shape of the vertical response spectrum based on regression is different from that of the horizontal component and complies with the recommended design vertical response spectrum of FEMA P-1050. V/H (vertical-to-horizontal ratios), as a main way to estimate vertical ground motion, cannot be simply fixed as 2/3. Therefore, site location, site condition, and frequency spectrum have to be considered comprehensively. The regression accuracy of the vertical ground motion of the multisource model is slightly higher than that of the point-source model and lower than that of the finite fault source model. It is expected that this model will serve as an alternative for source-to-site distance when multiple asperities are to be modeled in the absence of the detail fault model to get a general scenario of the future ground motions.

A pragmatic approach to adjusting early instrumental local magnitudes for seismic hazard assessments in Australia

Prior to the development of Australian-specific magnitude formulae, the 1935 magnitude correction factors by Charles Richter—originally developed for southern California—were almost exclusively used to calculate earthquake magnitudes throughout Australia prior to the 1990s. Due to the difference in ground-motion attenuation between southern California and much of the Australian continent, many earthquake magnitudes from the early instrumental era are likely to have been overestimated in the Australian earthquake catalogue. A method is developed that adjusts local magnitudes (ML) using the difference between the original (inappropriate) magnitude formulae (or look-up tables) and the Australian-specific formulae at a distance determined by the nearest recording station likely to have recorded the earthquake. Nationally, these adjustments have reduced the number of earthquakes of ML ≥ 4.5 in the early instrumental catalogue by approximately 25% since 1900, while the number of ML ≥ 5.0 earthquakes has reduced by approximately 32% over the same time period. The reduction in the number of moderate-to-large-magnitude earthquakes over the instrumental period yields long-term earthquake rates that are more consistent with present-day rates, since the development of Australian-specific magnitude formulae (approximately 1990). The adjustment of early instrumental magnitudes to obtain consistently derived earthquake catalogue is important for seismic hazard assessments.

Characteristics of strong ground motion attenuation in the 2019 Mw 5.8 Changning earthquake, Sichuan, China

A moderate magnitude earthquake with Mw 5.8 occurred on June 17, 2019, in Changning County, Sichuan Province, China, causing 13 deaths, 226 injuries, and serious engineering damage. This earthquake induced heavier damage than earthquakes of similar magnitude. To explain this phenomenon in terms of ground motion characteristics, based on 58 sets of strong ground motions in this earthquake, the peak ground acceleration (PGA), peak ground velocity (PGV), acceleration response spectra (Sa), duration, and Arias intensity are analyzed. The results show that the PGA, PGV, and Sa are larger than the predicted values from some global ground motion models. The between-event residuals reveal that the source effects on the intermediate-period and long-period ground motions are stronger than those on short-period ground motions. Comparison of Arias intensity attenuation with the global models indicates that the energy of ground motions of the Changning earthquake is larger than those of earthquakes with the same magnitude.

Evaluation of Key PSHA Assumptions—Case-Study for Romania

This case-study focuses on the analysis of several key assumptions necessary for the probabilistic seismic hazard assessment of Romania in the light of a future seismic hazard zonation of the territory. Among the aspects analyzed in this study are the appropriateness of the Poisson assumption which is tested on the earthquake catalogs of several seismic sources (crustal and the Vrancea intermediate-depth source), the azimuthal dependence of ground motion amplitudes from Vrancea intermediate-depth earthquakes and possible ground motion amplifications due to basin effects. The analyses performed in this study show that the Poisson distribution is able to model the observed earthquake frequency occurrence for the larger magnitude seismic events both for crustal and intermediate-depth seismic sources. Similar ground motion attenuation patterns irrespective of the azimuth with respect to the Vrancea intermediate-depth seismic source were observed only in the case of the 30 May 1990 earthquake, while in the case of the seismic events of 30 August 1986 and 31 May 1990 significant azimuthal ground-motion attenuation differences were observed. No significant differences in terms of ground motion amplitudes were observed at three seismic stations in Iasi area during the Vrancea intermediate-depth earthquakes of 30 May 1990 and 31 May 1990 possibly due to the limited elevation difference. Finally, significant long-period spectral amplifications were observed on the ground motions recorded at several sites from intramountainous depressions in Romania.

The Ground-Motion Attenuation Comparison: A case study for the 2017/05/11 Askale earthquake (Mw4.7)

Turkey is located on the Mediterranean-Himalayan seismic belt, which is the second largest earthquake zone in the world. Due to the fact that Erzurum basin is located in the Eastern Anatolia Region, it has a very complex structure in terms of its geological, tectonic and morphological features. Erzurum has been affected by destructive earthquakes throughout history. Some of these are Erzincan earthquake (26 December 1939), Horasan-Narman earthquake (30 October 1983), Spitak-Armenia earthquake (7 December 1988). In this study, the acceleration data of Erzurum-Aşkale (Mw=4.7) was used in order to estimate the peak ground acceleration using attenuation relationships. Attenuation relationships are important to determine how the peak ground acceleration decreases with distance. The data was recorded at twenty accelerometers in and around Erzurum. Peak ground accelerations were estimated according to Sadigh et al. (1997), Ambraseys et al. (1996), Kalkan and Gülkan (2004) attenuation relationships. As a result of calculations and comparisons, attenuation relationship of Sadigh et al. (1997) has found to be appropriate to the acceleration values recorded in the stations and has given the best results for the different soil types.

The 2018 national seismic hazard assessment of Australia: Quantifying hazard changes and model uncertainties

Seismic hazard assessments in stable continental regions such as Australia face considerable challenges compared with active tectonic regions. Long earthquake recurrence intervals relative to historical records make forecasting the magnitude, rates, and locations of future earthquakes difficult. Similarly, there are few recordings of strong ground motions from moderate-to-large earthquakes to inform development and selection of appropriate ground-motion models (GMMs). Through thorough treatment of these epistemic uncertainties, combined with major improvements to the earthquake catalog, a 2018 National Seismic Hazard Assessment (NSHA18) of Australia has been undertaken. The resulting hazard levels at the 10% in 50-year probability of exceedance level are in general significantly lower than previous assessments, including hazard factors used in the Australian earthquake loading standard ( AS 1170.4–2007 (R2018)), demonstrating our evolving understanding of seismic hazard in Australia. The key reasons for the decrease in seismic hazard factors are adjustments to catalog magnitudes for earthquakes in the early instrumental period, and the use of modern ground-motion attenuation models. This article summarizes the development of the NSHA18 explores uncertainties associated with the hazard model, and identifies the dominant factors driving the resulting changes in hazard compared with previous assessments.

PERBANDINGAN ATENUASI PERCEPATAN BATUAN DASAR DENGAN FUNGSI ATENUASI Mc Guire (1977), Campbell (1981), Idriss (1991) dan Ambraseys (1995)

Atenuasi getaran tanah (ground motion attenuation) adalah proses/ rumusan yang mana suatu gerakan tanah Y akibat gempa (percepatan, kecepatan, simpangan) ataupun intensitas gempa akan mengecil pada jarak yang semakin jauh dari sumber gempa, akibat redaman/ penyera-pan energi oleh massa batuan/tanah. Secara matematis, atenuasi getaran tanah adalah suatu hubungan antara jarak, R (episenter, jarak terdekat, jarak hipo-senter) dengan parameter gempa Y (percepatan, kecepatan, simpangan, intensitas gempa, ukuran gempa).Dari ketiga grafik diatas dapat disimpulkan bahwa nilai ground acc akan semakin kecil terhadap jarak epicenter. Hal ini sesuai dengan factor yang mempengaruhi atenuasi salah satunya yaitu jarak ke site (jarak episenter, jarak terdetak, jarak hiposenter).