Earthquake Time Research Articles

A new method for coseismic offset detection from GPS coordinate time series

Currently, the extraction of coseismic offset signals primarily relies on earthquake catalog data to determine the occurrence time of earthquakes. This is followed by the process of differencing the average GPS coordinate time series data, with a time interval of 3 to 5 days before and after the earthquake. In the face of the huge amount of GPS coordinate time series data today, the conventional approach of relying on earthquake catalog data to assist in obtaining coseismic offset signals has become increasingly burdensome. To address this problem, we propose a new method for automatically detecting coseismic offset signals in GPS coordinate time series without an extra earthquake catalog for reference. Firstly, we pre-process the GPS coordinate time series data for filtering out stations with significant observations missing and detecting and removing outliers. Secondly, we eliminate other signals and errors in the GPS coordinate time series, such as trend and seasonal signals, leaving the coseismic offset signals as the primary signal. The resulting coordinate time series is then modeled using the first-order difference and data stacking method. The modeling method enables automatic detection of the coseismic offset signals in the GPS coordinate time series. The aforementioned method is applied to automatically detect coseismic offset signals using simulated data and the Searles Valley GPS data in California, USA. The results demonstrate the efficacy of our proposed method, successfully detecting coseismic offsets from vast amounts of GPS coordinate time series data.

Rapid Detection of Co‐Seismic Ionospheric Disturbances Associated With the 2015 Illapel, the 2014 Iquique and the 2011 Sanriku‐Oki Earthquakes

AbstractCo‐seismic Ionospheric disturbances (CID, or “ionoquakes”) are disturbances in the electron density or total electron content (TEC) of the ionosphere, produced by the ground motion due to earthquakes. Usually, ionoquakes are detected in the near‐epicentral region within 8–10 min after an earthquake onset time. In this work, we present a new methodology that allows to estimate the CID arrival time based on determining the CID peak time in TEC measurements with respect to the peak time of seismic waves registered by the nearest seismic station. Our methodology also allows to understand the altitude of GNSS detection that otherwise remains ambiguous. We apply the newly developed techniques to detect CID signatures associated with three large earthquakes: the 2015 Illapel, the 2014 Iquique, and the 2011 Sanriku‐Oki. We show that for these events, the CID arrive 250–430 s after the time of the seismic wave peak, or 350–700 s after the earthquake onset time. Our analysis show that the first CID are detected at the altitudes of 150–180 km (the Sanriku earthquake) and of 200–300 km (the Illapel and the Iquique earthquakes). The disturbances represent high‐frequency acoustic oscillations that propagate with a horizontal speed faster than 0.75 km/s.

Paleoseismic evidence of five magnitude 7 earthquakes on the Norcia fault system in the past 8,000 years (Central Italy)

Many large-magnitude faults (6.5≤ Mw ≤7.2) of the Italian Apennines are characterized by multi-century return times, so historical sources may have missed their last earthquake or other predecessors. Hence, even in Italy, where seismic catalogs are among the most comprehensive and time-extensive worldwide, there is a need for complementary studies that might fill the lack of historical information and enhance the knowledge concerning the recurrence times of destructive earthquakes. As paleoseismology is the discipline that can do this, in this study, we present results collected in five new trenches opened along the 33-km-long Norcia fault system (central Apennines) where, in addition to the historically known 1703 earthquake (Mw 6.9), we uncovered indications of four Holocene predecessor, with a recurrence time of 1,825 ± 420 years. Considering also the paleoseismic results already published on the nearby Mt Vettore fault system (2016 earthquake of Mw 6.6), we guess that now the seismic hazard of this region could be assessed more robustly.

Characteristic analysis of earthquake sound signal based on wavelet transform

Earthquake is a kind of natural disaster with strong destructive power. As a kind of earthquake precursor signal, earthquake sound is of great significance of earthquake prediction. According to the characteristics of the earthquake sound signal, the earthquake sound monitoring data ten days before the earthquake was analysed using wavelet technology, the earthquake sound monitoring signals of different frequency bands was compared, and the change rule of the earthquake sound signal within ten days before the earthquake was emphatically studied. It was concluded that: the infrasound wave signal with normal fluctuation changed regularly into time; Ten days before the earthquake, the peak mutation of infrasonic signal occurred, which increased exponentially compared with the mean peak mutation value of earthquake sound signal. The number of this abnormal phenomenon increased to the shortening of the impending earthquake time, especially five days before the earthquake; The intensity of the earthquake sound signal in the frequency band of the infrasonic wave is gradually decreasing from the increase in the signal frequency. By studying the variation characteristics of earthquake sound signal with time before earthquake, it is of certain reference significance to study the correlation between abnormal ground earthquake signal and earthquake in earthquake prediction.

A neural encoder for earthquake rate forecasting

Forecasting the timing of earthquakes is a long-standing challenge. Moreover, it is still debated how to formulate this problem in a useful manner, or to compare the predictive power of different models. Here, we develop a versatile neural encoder of earthquake catalogs, and apply it to the fundamental problem of earthquake rate prediction, in the spatio-temporal point process framework. The epidemic type aftershock sequence model (ETAS) effectively learns a small number of parameters to constrain the assumed functional forms for the space and time correlations of earthquake sequences (e.g., Omori-Utsu law). Here we introduce learned spatial and temporal embeddings for point process earthquake forecasting models that capture complex correlation structures. We demonstrate the generality of this neural representation as compared with ETAS model using train-test data splits and how it enables the incorporation additional geophysical information. In rate prediction tasks, the generalized model shows >4% improvement in information gain per earthquake and the simultaneous learning of anisotropic spatial structures analogous to fault traces. The trained network can be also used to perform short-term prediction tasks, showing similar improvement while providing a 1000-fold reduction in run-time.

Earthquakes time series visualization in cilacap earthquake zone using QGIS and USGS data sets

Cilacap region earthquakes often occur with more than 5 Richter Scale. With these seismic conditions, earthquake studies in the Cilacap region will always be needed. These studies usually only have output in form of map visualization spatially, however, they have not been compiled in a time series. This study attempts to include visualization of spatial data in the form of a time-series. The data visualization was presented in form of graphs and maps. Graphical visualization using line bar graph type by applying descriptive statistics tries to determine the earthquake’s magnitude fluctuation. The other visualization in form of Heatmap map analysis applying the Kernel Density method is interpolated earthquake magnitude spatial data. The data used in this research was retrieved from the USGS datasets between 1918 to 2021. The spatial boundaries were taken from -7.324 ˚S, 107.941˚E to -10.407˚S, 111.116˚E. The results of spatial data visualization using the heatmap techniques were then analyzed temporally using the Temporal function in the QGIS software. The results of temporal analysis within a year are then sequenced into a video which is displayed on the following link https://youtu.be/m3B7HkfI8qY. The descriptive statistical analysis shows that Earthquakes have magnitudes ranging from 3.3 to 7.58 with a mean of 4.58 and a mode of 4.4. Heatmap analysis shows the results of earthquake magnitude interpolation with high density, located in the south of Cilacap and south of Yogyakarta. Also, the spatiotemporal analysis results show that there is a change in location trends that have high earthquake magnitude density values

An Optimum 1D Velocity Model for the Garhwal–Kumaun Himalaya Using Monte Carlo Style Inversion

Abstract A Monte Carlo based algorithm is developed to improve the 1D velocity inversion routines and minimize bias due to the choice of a starting model. Using this algorithm, a well-resolved six-layer minimum 1D velocity model, down to ∼24 km depth, is determined for the Garhwal–Kumaun Himalaya. A total of 4765 P- and 4724 S-phase travel times of local earthquakes recorded at 53 broadband seismic stations are used for this purpose. The travel time–distance curves from these carefully analyzed phase data of events are used to subsequently derive a prior 1D velocity model. Forward modeling of the travel time–distance curve yields an average Moho depth of ∼46 km and bulk crustal P- and S-wave velocity values of 7.60 and 4.47 km/s, respectively. To circumvent the subjectivity due to manual intervention in the inversion and automate the process, we propose a Monto Carlo style semirandom generation of initial trial velocity models, guided by the initial values derived from forward modeling. The estimated minimum 1D model reveals P- and S-wave velocities increasing from 5.17 to 6.85 km/s and 3.12 to 3.82 km/s, respectively, from the surface to a depth of 26 km. Subsequently, an optimum model is constructed for the region by incorporating the Moho layer in the minimum 1D model.

Improving the Estimation of the Occurrence Time of an Impending Major Earthquake Using the Entropy Change of Seismicity in Natural Time Analysis

This article is focused on a new procedure concerning a more accurate identification of the occurrence time of an impending major earthquake (EQ). Specifically, we first recapitulate that, as was recently shown [P. Varotsos et al., Communications in Nonlinear Science and Numerical Simulation 125 (2023) 107370], natural time analysis of seismicity supplemented with the non-additive Tsallis entropy Sq leads to a shortening of the time window of an impending major EQ. This has been shown for the Tohoku mega-EQ of magnitude M9 that occurred in Japan on 11 March 2011, which is the largest event ever recorded in Japan. Here, we also show that such a shortening of the time window of an impending mainshock can be achieved for major, but smaller EQs, of the order of M8 and M7. In particular, the following EQs are treated: the Chiapas M8.2 EQ, which is Mexico’s largest EQ for more than a century that took place on 7 September 2017 near the coast of Chiapas state in Mexico, the 19 September 2017 M7.1 EQ that occurred within the Mexican flat slab, and the M7.1 Ridgecrest EQ on 6 July 2019 in California.

Improving seimic hazard assessment in the Mediterranean Region

This paper is intended as a short presentation of the main limitations affecting seismic hazard assessment, revisiting possible methods available in the literature to be applied for this purpose. The convergence of the African Plate with the Eurasian Plate is the cause of the high seismic activity characterizing the Mediterranean region, with particular intensity in its eastern part. It is clear that the associated seismic risk requires appropriate measures for its mitigation. Seismic risk, the amount of resources that the community is expected to pay to earthquakes in the long term, is the product of three factors, such as seismic hazard, vulnerability and value of the exposed goods. As earthquakes cannot be prevented, seismic risk can be mitigated by improving our knowledge of seismic hazard, which is largely based on statistical analysis of historical earthquake catalogs. Nevertheless, historical records are affected by problems of reliability, completeness and shortness, as they commonly span time lengths of the same order of magnitude or even shorter than the inter-event time of the strongest earthquakes produced by specific seismic sources. In this respect, alternative methods can be proposed for integrating and improving our knowledge of seismogenic processes, and estimating both time-independent and time-dependent occurrence rates of strong earthquakes. We propose the application of physics-based earthquake simulators, requiring the knowledge of a robust geological-geophysical seismogenic model.

Seismic structure and its implication on the hydrothermal system beneath Mt. Ontake, central Japan

Mt. Ontake is an active volcano in central Japan where phreatic eruption activity is prominent. A shallow subsurface structure in the summit region of this volcano has been scarcely studied despite its importance. Our study examines the structure from three seismic analyses: a typical P-wave velocity from the semblance of the vertical propagation of intermediate-depth earthquakes (IDEs), a layered velocity model from P- and S-wave arrival times of shallow volcanic earthquakes, and a pseudoreflection profile from the autocorrelation functions of the IDEs. Our results consistently indicate the presence of three layers, which are interpreted as younger (> 0.1 Ma) and older (0.39–0.78 Ma) eruptive deposits and the basement. A comparison of the structure with hypocentres and deformation sources suggests fluid migration controlled by the structure.Graphical

Reduction of non-tidal oceanographic fluctuations in ocean-bottom pressure records of DONET using principal component analysis to enhance transient tectonic detectability

Ocean bottom pressure-gauge (OBP) records play an essential role in seafloor geodesy. Oceanographic fluctuations in OBP data, however, pose as a significant noise source in seafloor transient crustal deformation observations, including slow slip events (SSEs), making it crucial to evaluate them quantitatively. To extract the significant fluctuation phenomena common to multiple observation networks, including oceanographic fluctuations and tectonic signals, we applied principal component analysis (PCA) to the 3-year Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) OBP time series for 40 stations during 2016–2019. PCA could separate several oceanographic signals based on the characteristics of their spatial distributions, although evident transient tectonic signals could not be confirmed from the observed pressure records during this observed period. The spatial distribution of the first four principal components (PCs) reflected the common component, inclined component along sea depth, longitude component, and parabola-like pattern, respectively. By subtracting each PC (in particular, PC-2 and PC-4) from the time series, we could significantly reduce the sea depth dependence of OBP records, which has been highlighted in several previous studies and is also evident in this region. We interpreted PCs 2–4 as the reflection of the strength and meandering of ocean geostrophic currents based on a comparison with the PC spatial distribution of the numerical oceanographic models. In addition, to evaluate the ability of PCA to separate transient tectonic signal from OBP time series, including oceanographic fluctuations, we conducted a synthetic ramp assuming an SSE by rectangular fault and then applied PCA. The assumed synthetic tectonic signal could be separated from the oceanographic signals and included in the principal component independently depending on its amplitude, suggesting that the spatial distribution of each PC would change if the amplitude of the synthetic signal were sufficiently large. We propose a transient event-detection method based on the spatial distribution difference of a specific PC with or without a tectonic signal. We used the normalized inner product (NIP) between these PCs as the indicator of their similarities. This method can detect transient tectonic signals more significantly than the moment-magnitude scale of 5.9 from OBP records.Graphical

Correlation between small earthquakes and CO2 anomalies in spring waters: a statistical experiment on the probability of seismic occurrence

We correlated carbon dioxide (CO2) time series detected at the Gallicano site in Tuscany, Italy, with low-magnitude earthquakes occurred in the surrounding area between 2017 and 2021. The CO2 irregular component distribution was analyzed by a Pearson type VII fit, and its cumulate probability by the Gauss’s hypergeometric function, to statistically evidence anomalous fluctuations. We calculated the Matthews correlation between gas concentrations and low-magnitude earthquakes by defining a binary occurrence of CO2 anomalies and seismic events. A positive correlation was highlighted by a time lag between the digital series, which resulted in CO2 anomaly detections ahead of the earthquake time of two days. The correlated earthquakes were mainshocks of local magnitude 1.2 to 3.6, with epicenters within 40 km from the Gallicano site. Correlations among rainfalls, CO2 concentrations and earthquakes were also considered, showing that only few rainfall events were followed by a CO2 anomaly, mostly a day late.

Preventing extremity amputations after earthquakes: a quantitative analysis of fasciotomy and extrication time.

The purpose of this study is to evaluate the impact of prolonged extrication time and the time to fasciotomy applications on amputation requirement by giving quantitative and cutoff values. In this single-center study, the clinical records of patients with musculoskeletal injuries due to the 6 February Kahramanmaraş earthquake in Turkey were retrospectively reviewed. All patients who underwent fasciotomy or amputation regardless of age and gender were included in the study. 163 extremities of 140 patients who met the inclusion criteria were evaluated. Demographic data of the patients, such as age and gender, were recorded in this study. The primary outcome of this study was the correlation of the time between injury and fasciotomy applications with the amputation requirement. At the same time, the effect of prolonged extrication time of earthquake victims on amputation requirement. The mean age was 29.01 ± 15.55 of earthquake victims included in the current study and the gender distribution of the patients is almost equal. 87 amputations of 65 patients were performed and transtibial amputation was the most common type (41.3%). The mean fasciotomy time was 38.78 ± 23.64h. Delayed fasciotomies performed after 45.5h increase 28.48 times the amputation requirement. The mean extrication time in the current study was 36.49h. The patients with extrication time longer than 23h was associated with an 8.8 times higher risk of amputation. Authors believe that knowledge of the relationship between earthquake survivors' prognosis and time of extrication, as well as the impact of fasciotomy timing on extremity loss, is essential for a more successful treatment management in future disasters.

The Effect of Irregular Seismic Loading and Soil Density on the Liquefaction Behavior of Saturated Sand

Structures located on sandy soils can be significantly damaged by earthquake-induced liquefaction. A series of stress-controlled cyclic triaxial tests under harmonic and irregular loading under various soil densities 30%, and 50%, was conducted to evaluate the effects of irregularities and relative densities on the liquefaction characteristics of saturated sand. The irregular actual ground motions time histories obtained from six stations of the 1999 Chi-Chi Earthquake and harmonic sinusoidal cyclic loading time histories were applied to Firoozkooh #161 sand specimens, and the results were compared in terms of the type waveforms loading and relative densities. Based on the stress and energy method, the Correction coefficient is calculated for a variety of densities and types of irregular loading. The present results reveal that it is not precise to assume a single correction coefficient for all records, regardless of the complicated time-domain characteristics of ground motions. Furthermore, the results indicate that the relative soil density and the type of irregular loading influenced sand's pore pressure generation and liquefaction potential.

Islands of chaos in a sea of periodic earthquakes

Long paleoseismic records on mature faults suggest potentially chaotic recurrence patterns with cycles of strain accumulation and release that challenge simple slip- or time-predictable recurrence models. In apparent contradiction, the relatively small variability of earthquake recurrence times on these faults is often characterized as quasi-periodic, implying much regularity in the underlying mechanics. To reconcile these observations, we simulate one of the longest paleoearthquake records – the 24-event record from the Hokuri Creek site on the Alpine fault in New Zealand – using a physical model of rate- and state-dependent friction. In a parameter space formed by three non-dimensional parameters, a sea of parameters produces periodic earthquake recurrence behavior. Only a few models are characterized by fundamentally aperiodic recurrence patterns, in parametric islands of chaos. Complex models that produce partial and full ruptures of the Alpine fault can explain the earthquake recurrence behavior of the Alpine fault, reproducing up to 11 consecutive events of the Hokuri Creek paleoseismic record within uncertainties. The breakdown of the slip- and time-predictable recurrence patterns occurs for faults that are much longer than the characteristic nucleation size. The quasi-periodicity of seismic cycles is compatible with the nonlinear and potentially chaotic underlying mechanical system, posing an inherent challenge to long-term earthquake prediction.

Simplified engineering geomorphic unit-based seismic site characterization of the detailed area plan of Dhaka city, Bangladesh

Severe failure of improperly designed and poorly constructed structures may occur due to the amplified and prolonged ground motion during an earthquake, and hence prediction of the ground motion characteristics at the soil surface is crucial. In this study, based on the prepared simplified engineering geomorphic map, we performed a one-dimensional (1D) nonlinear site response analysis for seismic site characterization of the recently proposed Detailed Area Plan (DAP) area of Dhaka City, the Capital of Bangladesh. The engineering geomorphic unit-based map was prepared from image analysis and verified with the collected borehole data and surface geology map. The study area was classified into three major geomorphic units and seven sub-units subject to the subsurface soil profiles. Nine earthquake time histories, seven from the PEER NGA WEST2 data set and two synthetics, and seven identified subsurface soil profiles were used for nonlinear site response analysis, along with the BNBC 2020 uniform hazard spectrum as the target spectrum. For the selected earthquake ground motions, the near-surface soil response of the DAP area showed de-amplification of acceleration in the short period and amplification of acceleration in the long period. The amplified long-period acceleration could cause severe damage in inappropriately designed and poorly constructed long-period structures. The outcome of this study could be used to prepare a seismic risk-sensitive land use plan for the future development of the DAP of Dhaka City.

Positive Group Therapy Through Traditional Games with a Positum MGS Approach for Building Resilience Against Trauma in Times of Pandemics, War and Earthquakes: Theoretical Considerations and Practical Applications of “The Witches” Game

Why traditional games and how to transform them into powerful psycho-social and holistic instruments in Positive Group Therapy? The paper aims at looking at the space that Positive Transcultural Psychotherapy [PPT after N. Peseschkian, since 1977]TM can provide for the Positum MGS approach in utilizing traditional and transcultural games with a psycho-social aim in groups. Pandemics, wars and natural disasters such as earthquakes – among many other traumatic events – can result in forced displacement and migration for masses of populations, including children, and have severe consequences in the holistic health of affected people. The paper looks at the foundations of Positive Group Therapy, its interaction with the Positum MGS approach within it, and the value they can create for healing trauma in groups when integrating such tools as traditional games. The paper analised the research and practice in the field, demonstrating the great value of traditional and transcultural games in strengthening the identity and sense of belonging, as key resources for building resilience for individuals in groups and through group work sparked by traditional games transformed into psycho-social ones. The features, principles and strategies of the Positum MGS approach within the framework of PPT are further explained, and cases of practical application from recent years are discussed in the light of theoretical concepts of Positum MGS and PPT.

Statistical analogies between earthquakes, micro-quakes in metals and avalanches in the 1D Burridge-Knopoff model

Universalities and intriguing analogies in the statistics of avalanches are revealed for three physical systems defined on largely different length and energy scales. Earthquakes induced by tectonic scale dynamics, micro-scale level quakes observed from slipping crystallographic planes in metals and a one-dimensional, room-scale spring-block type Burridge-Knopoff model is studied from similar statistical viewpoints. The validity of the Gutenberg-Richter law for the probability density of the energies dissipated in the avalanches is proven for all three systems. By analysing data for three different seismic zones and performing acoustic detection for different Zn samples under deformation, universality for the involved scaling exponent is revealed. With proper parameter choices the 1D Burridge-Knopoff model is able to reproduce the same scaling law. The recurrence times of earthquakes and micro-quakes with magnitudes above a given threshold present again similar distributions and striking quantitative similarities. However, the 1D Burridge-Knopoff model cannot account for the correlations observed in such statistics.

ANALYSIS OF COULOMB STRESS TRANSFER AND EARTHQUAKE HAZARD IN THE ÇALDIRAN FAULT ZONE AND ITS ADJACENT REGION

Çaldıran fault zone (CFZ) are significant seismically active zone that generated many destructive earthquakes. In this fault system, the last of these major earthquakes occurred on 1976 (Ms = 7.3). Therefore, based on the seismotectonic b-value, earthquake probability, recurrence times and Coulomb stress changes, we investigate the future earthquake potential and positive/negative stress changes in this fault zone. The events with a magnitude greater than 3.6 are used to investigate stress transfer direction regarding the seismotectonic parameters. The results indicate that the regions having smaller b-values are obtained along with the SE of CFZ, whilst higher b-values are calculated around the east of Lake Van. On the other hand, the northeast of CFZ represents current stress accumulation. Similarly, the Coulomb stress variations of 1976 earthquake show that stress accumulated at different depths in the northwest of this fault system. In addition, considering the long-term slip rates and horizontal offset in previous studies, the recurrence time of earthquakes has approximately 302 years for a magnitude greater than 6.0. Finally, these comprehensive analyses explain the implications of seismic hazard evaluation and forecasting of possible next earthquake occurrences in this region.

Pre and Post Earthquake Slope Stability Analysis Using Equivalent Linear Method – a Case Study of Jure Landslide

Slope stability analysis is one of the most important tools to determine the stability of both natural as well as man-made slopes. The main objective of this study is to compare safety factor of the Jure landslide before and after an earthquake occurrence using Geostudio QUAKE/W module. Three different positions of water table (top, middle and bottom of debris) were considered for the study. The safety factors of both deterministic and probabilistic case are determined. The Gorkha Earthquake's time history data were taken into consideration. Both the bedrock and debris are modeled using the equivalent linear approach for dynamic analysis. The findings indicate that the slope was on the verge of failing prior to the earthquake and is predicted to fail following the earthquake event that was taken into account.