Earthquake Magnitude Research Articles

Analysis and Comparison of Fourier and Wavelet Transforms: Application for the Study of Seismic Source Parameters, Case of the 2001 Arequipa Earthquake

The purpose of this study is to apply the spectral analysis technique to the aftershocks of the 2001 Arequipa earthquake (Mw=8.4), based on the Fourier and Wavelet transforms.The data corresponds to the world network (IRIS), which has a station called NNA that is located in Peru. Together, 10 records corresponding to replicas registered during a period of 10 days after the main event have been analyzed. The methodology used in this study was based on the SAC software that stands for "Seismic Analysis Code". As a result of the Fourier transform, the fracture radius values obtained are in the range of 0.21 to 1.15km, the stress drop values for the analyzed aftershocks are between 0.60 to 38.08Mpa, the Energy Magnitude is from 3.36 to 4.42Me; for Wavelet: the frequency content which presents the values between 0.18 to 0.30 Hz, The maximum radiated energy between 25.70 to 40.80, the values obtained are in the range of 92.18 to 146.12s. The analysis and comparison of the transforms showed that with the Fourier transform different parameters can be determined by applying spectral analysis, however, with the wavelet transform the maximum radiated energy was determined This study contributes to the literature by finding these parameters of both transforms as it is of vital importance to determine the zones of energy accumulation that would cause earthquakes of great magnitude in the future.

Seismic characteristics of the 2022-2023 unrest episode at Taupō volcano, Aotearoa New Zealand

Taupō is a large caldera volcano located beneath a lake in the centre of the North Island of New Zealand and most recently erupted ~1800 years ago. The volcano has experienced at least 16 periods of unrest since 1872, each of which were characterised by increased seismic activity. Here we detail seismic activity during the most recent period of unrest from May 2022 to May 2023. The unrest was notable for the highest number of earthquakes detected during instrumented unrest episodes, and for one of the largest magnitude earthquakes detected beneath the lake for at least 50 years (ML 5.7). Relocated earthquakes indicate seismic activity was focused around an area hosting overlapping caldera structures and a hydrothermal system. Moment tensor inversion for the largest earthquake includes a non-negligible inflationary isotropic component. We suggest the seismic unrest was caused by the reactivation of faults due to an intrusion of magma at depth.

Scenario-based seismic hazard for horizontal and vertical ground motions in central Italy

We propose an innovative methodology for seismic emergency planning and earthquake risk mitigation in central Italy by integrating three prototypal earthquake scenarios. The different scenarios derive maximum earthquake magnitudes from different input data. The first scenario utilizes local rheological, geological, and geophysical conditions; the second scenario considers the study area fault characteristics, while the third scenario relies on the cluster analysis of historical and instrumental earthquake records. The magnitudes and related uncertainties are combined using a conflation method to derive the expected ground motions for a grid of sites in central Italy. The resulting scenarios include peak ground acceleration and spectral ordinates, presented as maps and spectra for two selected localities. The vertical component of ground motion is also presented, because it is essential for accurately assessing the response of short-period structures. Our methodology complements the more classic seismic hazard analyses, offering additional insights for earthquake contingency planning and loss analysis. The proposed methodology is flexible; multiple models and ongoing advancements in scenario practice (near-field effects, vertical ground motion, and the choice of ground motion models) can be easily incorporated, increasing the effectiveness of seismic scenario modeling in seismic emergency planning and risk mitigation.

Investigating worldwide strong motion databases to derive a collection of free-field records to select design-compatible waveforms for Switzerland

The process of choosing ground motions typically relies on assembling a collection of ground motions that match a desired spectrum. This selection process is guided by specific seismological criteria, including factors like earthquake magnitude, distance from the epicenter, site soil type, and the range of spectral periods that need to fit with the target spectrum. The selection algorithm and the available dataset of waveforms obviously play significant roles in this process. In many engineering and site response applications, it is essential that the input ground motion is representative for the shaking at the free surface of the Earth, and at times also a specific soil type may be required. However, real waveform databases often lack sufficient and/or consistent metadata related to the installation type and soil characterization of recording stations, as well as to the earthquake seismological parameters. This deficiency can lead to the selection of inappropriate waveforms, such as those recorded by stations situated within manmade structures (buildings, bridges, dams) or on a soil type different than the intended one. To address this issue, our approach for creating an appropriate waveform database applicable to Switzerland starts with the computation of seismic hazard disaggregation for return periods of 475 and 975 years. This computation helps identifying the magnitude-distance scenarios most relevant for the five seismic hazard zones defined in the Swiss building code. Once these magnitude-distance ranges are identified, we adhere to established standards regarding the quality control of three-component waveforms and their associated metadata. We assemble a database of waveforms by collating and homogenizing data from available global databases. In the interest of comprehensiveness, we also incorporate data obtained from 3D physics-based numerical simulations of strong-motion near the seismic source. Finally, we employ an algorithm that integrates the Eurocode 8 waveform selection criteria. This algorithm allows us to select and scale waveforms suitable for microzonation and structural analysis studies within each of Switzerland’s five seismic hazard zones. Selecting waveforms compatible with the target design spectra proves to be challenging due to the stringent criteria imposed by Eurocode 8. This challenge arises from the scarcity of recorded waveforms with verified metadata and precise site characterization in the desired magnitude-distance ranges.

The reliability assessment of the seismic demands of beams in chevron-braced frames and the factors affecting them

According to AISC 341–16, beams in chevron-braced frames should be designed for unbalanced forces. Several factors including the yield strength of steel materials, earthquake magnitude, the number of stories, and the details of the member connections affect the force applied to the beam. In this regard, the present study assessed the reliability of the seismic demand of beams in chevron-braced frames by considering the mentioned effective factors. First, 4-, 8-, and 12-story buildings representing low-, medium-, and high-rise buildings, respectively, were designed based on AISC 341–16. The beam-to-column connections and gusset plates were designed and modeled according to the capacity of the members. Then, one frame was selected from each building for stochastic seismic time-history analysis. For the stochastic analysis, 550 earthquake records were first chosen according to the considered characteristics of the site. Then, 100 ground motions were randomly selected and each braced frame was subjected to them. The yield and ultimate strengths of the steel materials were randomly selected based on the probability density function in each analysis. The results showed that a significant amount of the forces was generated in the beam-to-column connections contrary to the design assumptions. The results in the three frames showed that the resistance of the braced beams was on average higher than the demand forces. Moreover, the force distribution did not show an identical trend in different stories and the effect of the number of stories should also be considered in estimating the unbalanced forces of the braced beams.

Earthquake Detectability and Depth Resolution with Dense Arrays in Long Beach, California: Further Evidence for Upper-Mantle Seismicity within a Continental Setting

Abstract The Newport–Inglewood fault (NIF) is a slowly deforming fault cutting through a thin continental crust with a normal geothermal; yet it hosts some of the deepest earthquakes in southern California. The nucleation of deep earthquakes in such a continental setting is not well understood. Moreover, the deep seismogenic zone implies that the maximum NIF earthquake magnitude may be larger than expected. Here, we quantify the resolution of the Long Beach (LB) and the Extended Long Beach (ELB) dense arrays used to study deep NIF seismicity. Previous study of the regional catalog and of downward-continued LB array data found NIF seismicity extending into the upper mantle beneath LB. Later studies, which analyzed the ELB raw data, found little evidence for such deep events. To resolve this inconsistency, we quantify the array’s microearthquake detectability and resolution power via analysis of pre- and postdownward migrated LB seismograms and benchmark tests. Downward migration focuses energy onto the source region and deamplifies the surface noise, thus significantly improving detectability and resolution. The detectability is also improved with the increase in the array aperture-to-source-depth ratio. The LB array maximum aperture is only 20% larger than the ELB aperture, yet its resolution for deep (>20 km) events is improved by about a factor of two, suggesting that small changes to the array geometry may yield significant improvement to the resolution power. Assuming a constant aperture, we find the LB array maintain resolution with 1% of its sensors used for backprojection. However, the high-sensor density is essential for improving the signal-to-noise ratio. Analysis of the regional and array-derived NIF catalogs together with newly acquired Moho depths beneath the NIF suggests that mantle seismicity beneath LB may be a long-lived feature of this fault.

Potential domino effect of the 2023 Kahramanmaraş earthquake on the centuries-long seismic quiescence of the Dead Sea fault: inferences from the North Anatolian fault

Field observations conducted immediately following the February 6, 2023, Mw 7.8 Kahramanmaraş earthquake documented the southern surface rupture termination in the Amik Basin. The termination occurred in an en-echelon pattern, extending across the 3.5 km width of the approximately 10-km-wide stepover. This extension reached towards the northern tip of the Hacıpaşa Fault, which constitutes the main northern segment of the Dead Sea Fault Zone (DSFZ). Archaeoseismologic and paleoseismologic data show that the approximately 800-km-long DSFZ has been seismically quiet for more than 600 years in the north and 900 years in the south. A similar fault connection geometry at the western end of the 1939 Ms 7.9 Erzincan earthquake in the easternmost part of the North Anatolian Fault Zone and the subsequently triggered successive large magnitude earthquakes migrating westward within a few decades highlights an increased seismic hazard for the entire DSFZ. This heightened seismic hazard potential along the DSFZ, combined with historical population centers experiencing wars and migrations, puts millions of people at an unparalleled risk.

A Bayesian Merging of Earthquake Magnitudes Determined by Multiple Seismic Networks

Abstract We introduce a Bayesian algorithm designed to integrate earthquake magnitudes of the same type reported by various seismic networks, aiming to create unified and standardized catalogs suitable for widespread use. The fundamental concept underpinning this algorithm is the utilization of the inherent consistency within each individual network’s magnitude determination process. Assuming that the magnitudes for an earthquake measured by all networks conform to a Gaussian distribution, with a linear function of the unknown true magnitude serving as its mean, we derive the posterior probability distribution of the true magnitude under four different assumptions for the prior distribution: the uninformative uniform distribution, the unbounded Gutenberg–Richter (GR) magnitude–frequency law, the GR magnitude–frequency relationship restricted by the detection rate, and the truncated GR law as priors. We assess the robustness of the method by a test on several synthetic catalogs and then use it to merge the catalogs compiled by five seismic networks in Italy. The results demonstrate that our proposed magnitude-merging algorithm effectively combines the catalogs, resulting in robust and unified data sets that are suitable for seismic hazard assessment and seismicity analysis.

Deep carbonate gas reservoir sweet spot identification with seismic data based on dual-factor control of sedimentary facies and fault system

Deep carbonate reservoirs are attractive targets for gas development. These reservoirs are deeply buried, and commonly possess strong heterogeneity and poor seismic data quality, making the identification of favorable production areas (“sweet spots”) challenging. Furthermore, sedimentary facies and fault systems markedly impact reservoir quality, and identifying these features in seismic data is also crucial for sweet spot identification. To solve these problems, we propose a dual-factor-controlled sweet spot identification method with two steps. First, sedimentary facies and faults are identified separately at different seismic scales using different attributes by the steerable pyramid (SP) method. The SP method decomposes the original seismic data into high-frequency and low-frequency data. The amplitude attributes from high-frequency data are used to identify sedimentary facies, and coherence attributes based on low-frequency data are used to characterize the fault systems. Second, after separately identifying the sedimentary facies and faults, the two attribute volumes are merged together to identify reservoir sweet spots. The results are verified by using well production data. The results of a field study in the Dengying Formation deep carbonate reservoir in the central Sichuan Basin, China, indicate that reservoir sweet spots are primarily developed in ideal sedimentary facies along strike-slip fault systems. Sedimentary facies generally control the type and distribution of reservoirs, whereas strike-slip fault systems control the migration and accumulation of gas. In addition, the fault systems serve as karst channels that further improve the reservoir properties. The proposed dual-factor method might help to maximize exploration potential in deep carbonate reservoirs with similar settings.

Managing Intervention Works for Conservation and Revitalization: A Case Study of the Bârnova Monastery, Iași

This study offers insights into the management of intervention works aimed at conserving and revitalizing historical structures, focusing on the Bârnova Monastery in Iași, Romania. The study begins by contextualizing the broader challenges associated with preserving heritage churches and monastic buildings, elucidating the architectural characteristics and structural aspects typical of traditional Romanian Orthodox churches. Subsequently, the study delves into a detailed case analysis centered on the restoration of the medieval Bârnova Monastery, particularly its paramount structure, the Saint George Church, erected in the XVII century. This church exemplifies the traditional Orthodox architectural and structural norms prevalent during the medieval period. Through a structural diagnosis, the study identifies the vulnerabilities of the Saint George Church, which have been exacerbated by the impact of approximately 24 earthquakes of magnitudes exceeding 6.0 throughout its history. In response, a multifaceted approach to strengthening was devised, involving a combination of grouting and the installation of steel rods within vertically drilled galleries spanning the entire height of the walls. The adoption of this integrated strengthening strategy proved advantageous, significantly enhancing the seismic resilience of the church while simultaneously addressing the preservation needs of its historical features. This case study not only contributes to the body of knowledge on conservation and revitalization practices but also offers valuable insights into the effective management of intervention works for safeguarding heritage structures against seismic risks.

The impact of Kahramanmaraş (2023) earthquakes: A comparative case study for Adıyaman and Malatya

This study examines the effects of two major earthquakes of magnitude 7.7 and 7.6 that struck Kahramanmaraş on February 6th, 2023, followed by a magnitude 6.4 quake in Hatay on February 20th, which caused major damage in 11 Turkish provinces. The study focuses on Adıyaman and Malatya and uses an interdisciplinary approach to analyze the economic and environmental impacts. Primary data sources, including field visits and interviews, reveal clear labor-related challenges in both provinces, characterized by a government-induced labor shortage. In both provinces, physical capital has been severely damaged, particularly affecting small businesses, historic bazaars, and old industrial areas. The impact on businesses varies by size and location, with Adıyaman suffering more severe setbacks than other cities. The shortage of skilled labor related to the earthquake damage affects the quality of production, which can have a serious economic impact. Transportation disruptions continue to hamper supply chains and affect companies' ability to meet their export commitments. The environmental consequences, particularly the large amount of debris, pose a major challenge. The lack of a comprehensive disaster waste plan at the central government level leads to inadequate waste management. The study recommends sorting the debris at temporary sites to obtain reusable items while paying attention to the sustainability and transparency of debris management processes. In summary, this comparative case study highlights the need for tailored approaches to address the different impacts in the 11 provinces. A one-size-fits-all solution is insufficient and an individual needs assessment is needed for each province in order to implement targeted economic and environmental recovery measures.

A comparative study of SPT-based liquefaction potential estimation methods from three sites in India

ABSTRACT In the present study, four different SPT-based methods for liquefaction assessment namely Seed and Idriss (S–I), Tokimatsu and Yoshimi (T–Y), Japan Road Association (JRA), and Chinese code for Seismic Design of Buildings (CSDB) method has been discussed in detail. The present study compares the liquefaction potential estimation of S–I, T–Y, and JRA methods, respectively. The S–I method predicts 9.29 and 3.42 times higher liquefaction occurrence compared to JRA and T–Y methods respectively. Different damage indices such as liquefaction potential index (LPI), liquefaction risk index (LRI), and ground settlement have been evaluated for an earthquake magnitude of 7.5 on the Richter scale and peak ground accelerations varying in the range of 0.1–0.36 g respectively. LRI provides a more precise estimation of the liquefaction damages compared to LPI. The gradation of liquefiable soil has been presented and compared with the established limits of liquefiable soils.

Predicting the Magnitude of Possible Earthquakes in the Shahrood District of Khalkhal County, Ardabil, Iran, Using Artificial Neural Networks

Background and objective Earthquakes are natural disasters that can cause high damage. Prediction of earthquakes is necessary to reduce damages, develop resistant infrastructure, and prevent the loss of life in human societies. This research aims to predict the magnitude of possible earthquakes in the Shahrood district of Khalkhal County using artificial neural networks (ANN). Method A multi-layer perceptron neural network was used to predict earthquake magnitude. Results The results showed that in the fault areas, especially the Kalur fault, earthquakes with a magnitude of 1-3 on the Richter scale are more likely to occur (70%). The likelihood of earthquakes with a magnitude of 4-6 on the Richter scale is moderate (26%) and the earthquakes with a magnitude of 7-10 on the Richter scale have a very low probability (4%). Conclusion In future studies, it is recommended to use machine learning models to better and more accurately predict earthquakes in the studied area.

A Numerical Consideration on the Correlation Between Magnitude of Earthquakes and Current Intensity Causing ULF Electromagnetic Wave Emission

A Numerical Consideration on the Correlation Between Magnitude of Earthquakes and Current Intensity Causing ULF Electromagnetic Wave Emission

Rupture Model of the 5 April 2024 Tewksbury, New Jersey, Earthquake Based on Regional Lg-Wave Data

Abstract On 5 April 2024, an earthquake of magnitude 4.8 occurred in Tewksbury, New Jersey. It was the largest instrumentally recorded event since 1900 in New Jersey and southern New York. Millions of people around New York City, ∼65 km east-northeast of Tewksbury, felt the shaking from the mainshock, but the epicentral area experienced no known significant property damages. We determine the focal mechanism, which is oblique faulting, and retrieve the Lg-wave relative source time functions (RSTFs) from the stations at regional distances to understand rupture processes and ground motions. Our fault-slip models well explain azimuthal variations of the RSTFs. The models show the rupture propagating toward the east-northeast (∼50° to 60°), not along the fault strike. The slip distribution on the nodal plane striking north and dipping to the east shows a slip area of 1.1 km radius with the rupture propagating down-dip. The down-dip rupture may account for the observed lack of strong shaking in the epicentral area.

<p>A Catalogue of Historical and Instrumentally-Recorded M<sub>s</sub> ≥ 7 Earthquakes in Taiwan</p>

A catalogue of forty-nine instrumentally-recorded earthquakes with magnitudes ≥ 7 in Taiwan from 1906 to date is compiled from regional and international catalogues and literature. Included also are seven historical earthquakes that occurred from 1792 to 1867. The earthquake magnitude is the surface-wave magnitude, Ms. The moment magnitude, Mw, is also evaluated either from Ms or obtained from related documents. Except for one event, Mw is smaller than or equal to Ms. There are the ‘doublets’, ‘triplets’, and ‘quadruplets’ in these earthquakes. The spatial distribution of epicenters shows that most of the events occurred in offshore eastern Taiwan and only a few inland events happened in western Taiwan. The shortest inter-occurrence time between two consecutive events is less than 1 day; while the longest one is 5742 days between No. 47 event and No. 48 event. The inter-occurrence time somewhat increases with time. The time series of earthquakes shows irregular recurrence behavior with aperiodicity, fractality, and a weak memory effect. The damage produced by earthquakes is much higher from inland events (mainly in western Taiwan) than from offshore ones.

Magnitude-corner frequency distribution of explosion earthquakes: a case study of Anak Krakatau Volcano, Sunda Strait

Abstract We investigated the distribution between the magnitude and corner frequency of explosion earthquakes at the Anak Krakatau volcano during June - July 2014. We analyzed 100 explosion waveforms recorded at the KRA3 and KRA4 seismic stations located approximately 0.55 km and 3.84 km away from the active crater, respectively. We observed a relationship between the moment magnitude and the corner frequency of the explosion earthquake distribution. The result shows that the moment magnitude is inversely proportional to the corner frequency in a logarithmic scale using the full waveform of explosion earthquakes. The distribution equation of full waveform (0-20s) at KRA3 and KRA4 as follows; fc = −2.72145 log(Mw ) + 7.99523, and fc = −1.13971 log(Mw ) + 5.97855 respectively. The magnitude range is approximately 1.5–3 Mw. Meanwhile, the corner frequency range is about 4-8 Hz. Our result shows a similar distribution to those in the tectonic earthquake and volcano studies at different locations which is the magnitude is inversely proportional to the corner frequency. We also observed the relation between seismic moment and corner frequency which shows that the seismic moment is inversely proportional to the corner frequency with the range of seismic moment is about 1013-1015 N.m. Meanwhile, the stress drop is proportional to the corner frequency with the range of stress drop is about 100 and 103 bar. Our results are similar to those of other studies. These parameters show the basic statistical properties of volcanic eruptions. This study is important for understanding the dynamics of volcanic eruptions at the Anak Krakatau volcano.

Post-Earthquake Liquefaction Vulnerability Mapping by Swedish Weight Sounding and Standard Penetration Test

On September 28, 2018, a 7.5-magnitude earthquake struck Palu City, Sigi Regency, and Donggala Regency in Central Sulawesi. It triggered liquefaction in different locations, including Balaroa, Petobo, Jono Oge, and Sibalaya; Typically, a significant number of studies conducted in the Balaroa region relied on a small amount of field test data to cover a rather large area. This research aims to map the liquefaction vulnerability by analyzing the data from both the Swedish Weight Sounding (SWS) and the Standard Penetration Test (SPT) in the Balaroa area. The SWS data was acquired through mapping using a systematic grid sampling method at ten different locations. The liquefaction potential was analyzed based on the N values by converting the SWS data (Nsw and Wsw) to Nvalues using the Inada equation (1960). Afterward, the analysis findings were verified by comparing them with the SPT data obtained from the same area. Based on the SWS and SPT data analysis results, all locations, including the adjacent areas, exhibited very high liquefaction vulnerability. In contrast, the SPT data indicated that the areas further from the spots exhibited low and very low liquefaction. The findings indicated that the occurrence of post-earthquake liquefaction in Balaroa and other regions within Palu City is prone to recurrence following earthquakes of specific magnitudes. Doi: 10.28991/CEJ-2024-010-07-09 Full Text: PDF

Probabilistic Seismic Hazard Assessment of Sitamarhi near the Central Himalayan Region

ABSTRACT Sitamarhi, situated in the North-Bihar region of the Himalayan foothills is one of the seismically vulnerable regions of India. This region faced several devastating earthquakes, such as the 1934 and 1988 Bihar Nepal earthquake and the 2015 Nepal earthquake due to the movement of tectonic plates. The purpose of the present study is to exhibit the uniform hazard spectrum (UHS) and peak ground acceleration (PGA) values based on the probabilistic seismic hazard method using different seismotectonic parameters. The Gutenberg Richter (G-R) seismicity parameters ‘a’ and ‘b’ were estimated on the basis of regional earthquake magnitude data for the studied region. Regional earthquakes data were taken from the United States Geological Survey (USGS), International Seismological Centre (ISC), Indian Meteorological Department (IMD), and Seismotectonic Atlas of India. The region of interest for the probabilistic seismic hazard analysis (PSHA) is within a 500 km radius considering past seismicity and 62 seismotectonic sources which were identified in the study area. Large-scale geological features were utilised to describe the regional seismic source zones, which were used to derive the relationship between return period and ground motion parameters. Estimated PGA values are 0.92g for 2% and 0.68g for 10% probability of exceedance in 50 years time period, respectively. This research infer that the West Patna fault (WPF) and Sitamarhi fault (SMF) are the two maximum contributors in PGA for the Sitamarhi region.

Inferring maximum magnitudes from the ordered sequence of large earthquakes.

The largest magnitude earthquake in a sequence is often used as a proxy for hazard estimates, as consequences are often predominately from this single event (in small seismic zones). In this article, the concept of order statistics is adapted to infer the maximum magnitude ([Formula: see text]) of an earthquake catalogue. A suite tools developed here can discern [Formula: see text] influences through hypothesis testing, quantify [Formula: see text] through maximum likelihood estimation (MLE) or select the best [Formula: see text] prediction amongst several models. The efficacy of these tools is benchmarked against synthetic and real-data tests, demonstrating their utility. Ultimately, 13 cases of induced seismicity spanning wastewater disposal, hydraulic fracturing and enhanced geothermal systems are tested for volume-based [Formula: see text]. I find that there is no evidence of volume-based processes influencing any of these cases. On the contrary, all these cases are adequately explained by an unbounded magnitude distribution. This is significant because it suggests that induced earthquake hazards should also be treated as unbounded. On the other hand, if bounded cases exist, then the tools developed here will be able to discern them, potentially changing how an operator mitigates these hazards. Overall, this suite of tools will be important for better-understanding earthquakes and managing their risks. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'.