Epicenter Location Research Articles

Developing a "Disaster Scenario" to prepare for the possibility of disruptions to maritime transportation serving coastal communities of Vancouver Island

Planning for a crisis scenario that interferes with supply chain operations aims to speed up the recovery process. How to reduce disruptions in marine supply networks, especially in coastal communities, has not received adequate research. Therefore, in this research, a catastrophe scenario is created following consultations with a marine stakeholder and a marine geologist, and its viability is then evaluated by two maritime professionals. The scenario for the Fraser River is developed on the British Columbian island of Vancouver. The river's delta is susceptible to underwater landslides since it is composed of 65 % mud and clay and 35 % sand. Following an earthquake in Cascadia Subduction Zone, an underwater landslide may happen at low tide. This forecast makes sense since, as mentioned in earlier research, there is a strong likelihood that an earthquake of magnitude 9.0 with an epicentre location roughly 300 kilometres from Vancouver may occur. It is also anticipated that an underwater landslide with a retrogression toward the land of 450 m would take place according to the developed scenario of this research. Landslides in the Fraser River are likely to be at a location near to Sand Heads Lighthouse since large-scale earthquakes may trigger them. For example, the landslide developed in 1985 was around 100 m away from the Lighthouse. Thus, one of the main outcomes of the scenario is the destruction of the Sand Heads Lighthouse and the buoys from the outer delta. Additionally, the planned scenario may destroy structures along the coast, such as shipyards, quaysides, and other buildings. The Fraser River is mainly used by ferries and barges to bring foods from the mainland to Vancouver Island; as a result, the islanders place a great deal of reliance on this river to support their way of daily life. 90 % of their foods comes from outside the island, and there is only a three-day supply of fresh food in the shops. This signifies the importance of the Fraser River.

APPRAISAL OF THE ABAJI-ABUJA (NIGERIA) ML 2.25 EARTH-TREMOR OF 10th JANUARY 2020

This research aims at determining the epicentre, magnitude and energy dissipated during the earth-tremor which took place at Abaji-Abuja (Nigeria) on 10th January 2020 at 13:46:20 UTC. The event was recorded by Volksmeter II VMII-2RU broadband Seismographs located at the Earthquake and Space Weather laboratory, Obafemi Awolowo University, Ife, Osun state, Nigeria. The computed P-wave and S-wave arrival times and lag times were 35.8seconds, 36.1seconds and 33.3seconds recorded by three Seismographs Ife (1), Ife (2) and Ife (3) respectively. The WinQuake software was used for the analysis. Epicentre distances computed were 330.3 km, 333.5 km and 303.2 km from the three seismograms, using trilateration method. The results gave the epicentre location at 8049’N and 6047’E (Gurdi town, Yaba District, Abaji LGA, Abuja, Nigeria),focal depth of 5 km, and average epicentral distance of 322.3km from Ile-Ife. The tremor has a Local Magnitude of 2.25 MLand Coda Magnitude of 3.7Md, and the dissipated energy of 149.6 × 10-12 KJ. The implication of these results is that a local magnitude of 2.25 ML of 149.6 × 10-12KJ of energy serves as an indicator to the future occurrence of another earthquake within the said region. Necessary precautionary measures should be taken when carrying out geological and construction works within the Abaji-Abuja environs. The massive rock blasting and quarrying must have reactivated the faults within the area.

Possible Locking Shock Time in 2–48 Hours

An hourly scale precursor of inland earthquakes (EQs) is revealed in this paper. Several EQ cases in China have been reported. As indicated by a table listing 23 inland EQs and their shock time, epicenter location, magnitude, near-epicenter weather conditions, precursor start time and precursor duration, when the weather conditions are fair near the epicenter, an anomalously negative atmospheric electrostatic signal is readily observable approximately 2–48 h before the EQ occurs. Moreover, a successful single-station alarm for nearby moderate-magnitude EQs is demonstrated, and a possible mechanism for the precursor signal is proposed. The change in the electrostatic field during an EQ process is explained as the release of radioactive gases from the subsurface into the atmosphere via large (regional-scale) preexisting microfractures in the rock at the source depth. These gases considerably ionize the atmosphere, and the separated positive and negative ions establish a special macroscopic electric field. The final critical stage of 2–48 h before an EQ may indicate a stable tectonic process.

The 2021MW 6.2 Mamuju, West Sulawesi, Indonesia earthquake: partial rupture of the Makassar Strait thrust

SUMMARYOn the 2021 January 15 (local date), an MW 6.2 earthquake struck the Mamuju and Majene regions of West Sulawesi, Indonesia. This event killed more than 100 inhabitants, leaving at least 30 000 people displaced from their homes, and damaged almost 8000 buildings within a radius of ∼30 km from the main shock's epicentre location (as shown on our damage proxy map). This event was generated by an active fault that continues to the Makassar Strait Thrust (MST) offshore West Sulawesi. The hazard potential of this fault remains poorly understood. In this study, we use seismic and Global Positioning System (GPS) data to investigate the source characteristics of the main shock. The results suggest that the main shock partially ruptured one segment of the MST, activated a secondary fault structure, and likely brought the updip unruptured section of the MST segment closure to failure. Our analysis of interseismic GPS velocities indicates that the Mamuju and Majene regions have a higher crustal strain rate than other nearby regions. The results (partial rupture of the MST segment, the updip unruptured section of the MST and high strain rate in the Mamuju and Majene regions) together suggest a significant seismic hazard potential in West Sulawesi, particularly in the Mamuju and Majene areas.

SEISMICITY of KAMCHATKA and COMMANDER ISLANDS in 2016–2017

The seismicity review of Kamchatka and surrounding territories for 2016–2017 is given. In the Kamchatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=4.0, and for earth-quakes with h≥350 km under the Okhotsk sea MLmin=4.3. The Kamchatka catalogue of earthquakes with ML=3.6–7.3 for 2016–2017, published in the Appendix to this article, includes 2898 events. 191 earthquakes of the catalogue were felt in Kamchatka and surrounding areas with seismic intensity I=2–6 according to the MSK-64 scale. For all events with ML≥5.0 that occurred in 2016–2017 within the area of responsibility of Kamchatka branch of Geophysical Survey RAS, an attempt to calculate the seismic moment tensor (SMT) was made. There are 109 such events in the regional catalogue. For 102 earthquakes the SMT and depth of the equivalent point source were calculated. The calculations were performed for the SMT double-couple model using a nonlinear algorithm. The level of seismicity according to the “SOUS'09” scale in 2016 corresponds to the “background increased”, for 2017 it is also the “background increased”, but within the assessment accuracy – “high”. In 2016–2017 within the Kamchatka branch area of responsibility, an atypical pattern of the location of earthquake epicenters was observed due to the occurrence of two strong events – the Near Aleutian (Mw=7.8, July 17, 2017) and South Ozernovsky (Mw=6.6, March 29, 2017) earthquakes and their aftershock processes.

Mapping of lymph node dissection determined by the epicenter location and tumor extension for esophagogastric junction carcinoma.

Previous studies identified the extent of lymph node dissection for esophagogastric junction (EGJ) carcinoma based on the metastatic incidence. The study aimed to determine the optimal extent and priority of lymphadenectomy based on the therapeutic efficacy from each station. The studies on the lymph node metastasis (LNM) and therapeutic efficacy index (EI) for EGJ carcinomas were identified until April 2022. The obligatory stations with the LNM rates over 5% and therapeutic EI exceeding 2% should be routinely resected for D2 dissection, whereas the optional stations with EI between 0.5% and 2% should be resected for D3 dissection in selective cases. The survey yielded 16 eligible articles including 6,350 patients with EGJ carcinoma. The metastatic rates exceeded 5% at no. 1, 2, 3, 7, 9, 11p, and 110 stations and were less than 5% in abdominal no. 4sa~6, 8a, 10, 11d, 12a, and 16a2/b1 and mediastinal no. 105~112 stations. Consequently, obligatory stations with EI over 2% were largely determined by the epicenter location and located at the upper perigastric, lower mediastinal, and suprapancreatic zones, corresponding to those with rates of LNM over 5%. Consistent with the LNM rates less than 5%, the optional stations with EI between 0.5% and 2% were largely dependent on the degree of tumor extension toward the lower perigastric, splenic hilar (grecurvature), para-aortic (less curvature of the cardia), and middle or upper mediastinal zones. The obligatory stations can be resected as an "envelope-like" wrap by transhiatal proximal gastrectomy with lower esophagectomy, whereas the optional stations for dissection are indicated by the tumor extension. The extended gastrectomy is required for the lower perigastric in the stomach-predominant tumor with gastric involvement exceeding 5.0cm, para-aortic dissection in the less curvature-predominant tumor and splenic hilar dissection in the grecurvature-predominant tumor whereas transthoracic subtotal esophagectomy is required for complete mediastinal dissection and adequate negative margin in the esophagus-predominant tumor with esophageal invasion exceeding 3.0cm.

Spatio‐temporal variation in b‐value prior to the 26 November 2021 Mizoram earthquake of northeast India

In this study, the variation in frequency magnitude distribution factor (b‐value) before the main shock has been assessed for the 26 November 2021 Mizoram earthquake (Mw 6.1) in northeast India. The study area covering the Indo‐Burma Ranges is divided into square grids of equal dimension and spatial mapping of the b‐value for each square grid has been carried out. The maximum likelihood method is implemented for the estimation of the b‐value of each grid. The epicentral location of the 26 November 2021 Mizoram earthquake (Mw 6.1) is found to be in the intermediate b‐value square grid. The temporal variation in the b‐value indicates a considerable decline in the b‐value before the occurrence of the main event. The depth‐wise variation in the b‐value suggests an antithetical relationship between the b‐value and crustal stress. The spatio‐temporal and depth‐wise fluctuation in the b‐value results have been strengthened by employing a non‐parametric Kolmogorov–Smirnov (K–S) test. Based on our study, we infer that interplate earthquakes occur mostly in the upper crust of the study region.

The Influence of Cumulative Intensity on Macroseismic Source Parameters: The Case of 2016–2017 and 1703 Seismic Sequences (Central Italy)

AbstractThe macroseismic source parameters of earthquakes occurring within a sequence are strongly influenced by cumulative damage effects. When we deal with historical seismic sequences, in addition to the cumulative intensities, other intrinsic uncertainties due to the scarcity and indeterminacy of sources come into play. These issues imply that the parameterizations of the single earthquakes within a historical seismic sequence are not univocal and that all the uncertainties that are addressed when assessing macroseismic intensity should be carefully considered in the parameter estimation. In the light of these considerations, we performed some tests on the 2016–2017 and 1703 seismic sequences, which occurred in the same area in central Italy, to compute the macroseismic source parameters by means of two independent methods. Results show that the cumulative effects arising from multiple damaging earthquakes can cause biases in the intensity assessments, which affect the computed magnitude and epicentral locations. To reduce bias in macroseismic intensities due to cumulative damage, we illustrate a simple procedure, called cumulative intensity subtraction (CIS), which consists in discarding the localities strongly damaged by the early earthquakes of a sequence from the intensity distributions used for computing the macroseismic source parameters of the subsequent earthquakes. The outcomes show that, for the 2016 seismic sequence, the CIS approach provides locations in agreement with the instrumental epicenters and with the causative faults. For the 1703 sequence, the CIS approach along with explicit accounting for the indeterminacy in intensity assignments give a range of equally plausible solutions. The CIS represents an exploration of a simple strategy that stems from an attempt to give significance to macroseismic intensity in the presence of cumulative damage.

Co- and Postseismic Deformation of the 2020 Mw 6.3 Nima (Tibet, China) Earthquake Revealed by InSAR Observations

On 22 July 2020, an Mw 6.3 earthquake occurred in Nima County, central Qinghai-Tibet Plateau, China. We used the synthetic aperture radar interferometry (InSAR) technique with Sentinel-1 images to retrieve the line of sight (LOS) coseismic deformation fields which indicate that the maximum surface displacement reached ~30 cm. We then processed a series of interferograms spanning one year after the Nima earthquake with the Small Baseline Subset Interferometric SAR (SBAS-InSAR) technique. The maximum cumulative postseismic LOS surface displacement reached ~8 cm and approximately followed a logarithmic function over time. The inversion of the fault geometry and co- and afterslip distribution shows that the epicenter location was (33.18°N, 86.88°E) at a depth of 7.4 km, and the causative fault had an N29.1°E strike and 50.2° dip. The most coseismic slip was concentrated at depths between 3 to 12 km with a peak value of 2.0 m at 7.4 km, whilst most afterslips were concentrated at depths between 0 to 12 km with a peak value of 0.2 m at 5 km. The postseismic moment energy was about 5.04 × 1017 N∙m 308 days after the event, which was approximately 13.8% of the coseismic moment energy. By analyzing the contribution of afterslip and poroelastic rebound to postseismic deformation, it was concluded that afterslip was the main early postseismic deformation mechanism. Future attention should be paid to the northern segment of the West Yibug Caka fault and East Yibug Caka fault.

Spatio-temporal analysis of b-value prior to 28 April 2021 Assam Earthquake and implications thereof

Here, we report a Spatio-temporal analysis of the frequency magnitude distribution of earthquakes (b-value) before the 28th April 2021 (Mw 6.4) earthquake event observed in northeast India. To esti- mate the average b-value for the study region, a data set of 750 earthquake events with magnitude Mw ≥ 3.9 is extracted from the homogenous part of the earthquake catalog (1950-2021) documented by the United States Geological Survey (USGS) and International seismological center (ISC) in the region. For spatial analysis of the disparities in b-value, the whole study region is subdivided into 16 square grids of dimension 1o×1o and the b-value is calculated for each subsection. In congruence with other studies, this work yields b-values ranging from 0.66 to 1.25. After the calculation of the b-value for each grid, it is observed that the grid with the epicentral location of the 28th April 2021 (6.4) earthquake has a low b-value. Accordingly, the spatial correlation and aberrant pattern between b-value and focal depth have been comprehensively explored. It is observed that the b-value sig- nificantly dips within a depth range of ~15-35 km which implicates high-stress accumulation and crustal homogeneity. The depth-wise variation in b-value infers the antithetical relationship between b-value and crustal stress. Mostly interplate earthquakes are observed in the study region; thereby hinting at intense seismicity at the upper crust.

Quaternary deformation patterns in East–Central Iran, constrained by coseismic–postseismic displacements of the 2017 Hojedk triplet earthquake in the Kerman Province

The Central Iranian Microcontinent (CIM) in east-central Iran is located north of the active Arabia–Eurasia collision zone. Here, we report on the structure, deformation patterns, and earthquake occurrences along the dextral Lakar–Kuh and Godar fault systems in the CIM. The geometry of these fault systems marks a major restraining bend responsible for surface and rock uplift in the Plio–Pleistocene that produced the Mian Kuh mountain range. The 2017 Hojedk triplet earthquake (Mw = 5.8–6.0) occurred in the Mian Kuh Range. Sentinel–1 A Interferometer Synthetic Aperture Radar (InSAR) images (descending and ascending) were used to extract the coseismic displacements associated with the earthquake and its aftershocks. The results indicate a maximum displacement of ∼20 cm, corresponding to hanging wall uplift along the radar Line-of-Sight (LOS) direction. The Geodetic Bayesian Inversion (GBIS) of the coseismic deformation indicates that the causative faults of the Hojedk earthquakes were two reverse faults with NW–SE–strikes and SW–dips, with minor dextral slip components. Given the focal mechanism solutions and the epicenter locations of the triple earthquake sequence, we infer that these faults at the southern termination of the Lakar–Kuh Fault represent two segments (with different dip angles) of a previously unrecognized, blind reverse fault (a splay of the Godar Fault at depth). The Hojedk Earthquake and the geometry and kinematics of its causative faults highlight the strong potential of seismic hazard zones along the strike-slip fault systems in the CIM.

Hazard and Risk-Based Tsunami Early Warning Algorithms for Ocean Bottom Sensor S-Net System in Tohoku, Japan, Using Sequential Multiple Linear Regression

This study presents robust algorithms for tsunami early warning using synthetic tsunami wave data at ocean bottom sensor (OBS) arrays with sequential multiple linear regression. The study focuses on the Tohoku region of Japan, where an S-net OBS system (150 pressure sensors) has been deployed. To calibrate the tsunami early warning system using realistic tsunami wave profiles at the S-net stations, 4000 stochastic tsunami simulations are employed. Forecasting models are built using multiple linear regression together with sequential feature selection based on Akaike Information Criterion and knee-point method to identify sensors that improve the accuracy most significantly. The study considers tsunami wave amplitude at a nearshore location and regional tsunami loss for buildings to develop hazard-based and risk-based tsunami warning algorithms. The models identify an optimal configuration of OBS stations and waiting time for issuing tsunami warnings. The model performance is compared against a base model, which only uses the earthquake magnitude and epicenter location. The result indicates that estimating the tsunami amplitude and loss via S-net improves accuracy. For the hazard-based forecasting, adding six sensors from the S-net improves the accuracy of the estimation most significantly with an optimal waiting time of 3 min. For the risk-based forecasting, a longer waiting time between 5 and 10 min is suitable.

Chinese Nationwide Earthquake Early Warning System and Its Performance in the 2022 Lushan M6.1 Earthquake

As one of the most earthquake-prone regions in the world, China faces extremely serious earthquake threats, especially for those heavily populated urban areas located near large fault zones. To improve the ability to prevent and minimize earthquake disaster risks, and to reduce earthquake disaster losses, China is currently building a nationwide earthquake early warning system (EEWS) with the largest seismic network in the world. In this paper, we present the newest progress of this project through describing the overall architecture of the national EEWS and evaluating the system performance during the 2022 Lushan M6.1 earthquake. The accuracy of the source characterization for the Lushan earthquake is discussed by comparing the continually estimated location and magnitude with the catalogs obtained from the China Earthquake Networks Center. For this earthquake, the EEWS generated a total of five alerts, and an initial alert was created 5.7 s after its occurrence, with excellent epicentral location and origin time estimation. The final alert was issued 16.5 s after origin time with a magnitude estimate of M6.1, the same as the catalog value. However, from the point view of alerting performance, the radius of the real blind zone without warning time was about 30 km and much larger than the theoretical result, mainly caused by the releasing system not considering the epicenter distance of each terminal when issuing the alerts. Although the earthquake exposed some limitations that need to be addressed in future upgrades, the results showed that most aspects of the EEWS presented a robust performance, with continuous, reliable event detections and early-warning information releasing.

Rapid Source Determination of the 2021 Mw 7.4 Maduo Earthquake by a Dense High-Rate GNSS Network in the Tibetan Plateau

Abstract High-rate Global Navigation Satellite Systems (GNSS) observations from an integrated network in the Tibetan plateau were used for rapid source determination of the 2021 Mw 7.4 Maduo earthquake. Constrained by high-rate displacements from nine stations near the source, the magnitude was essentially determined as early as 20 s after the origin time (OT), whereas the 39-s-long rupture propagated only approximately halfway, and together with the epicenter location and rupture length, they were completely determined 29 s after the OT or 10 s before the rupture completion. In addition, to test the capability and feasibility of current GNSS networks for rapid source determination in the Tibetan plateau, two experiments were further implemented to invert source parameters by real observations at farther sites and synthetic observations induced by an Mw 7.0 modeled earthquake. The results demonstrate that current GNSS networks are capable and feasible to provide rapid source determination and earthquake early warning in approximately 30 s after the OT for large earthquakes (Mw 7.0+) based on current station density, spatial coverage and communication conditions in the Tibetan plateau.

Multi-array analysis of volcano-seismic signals at Fogo and Brava, Cape Verde

Abstract. Seismic arrays provide tools for the localization of events without clear phases or events outside the network, where the station coverage prohibits classical localization techniques. Beam forming allows the determination of the direction (back azimuth) and horizontal (apparent) velocity of an incoming wavefront. Here we combine multiple arrays to retrieve event epicentres from the area of intersecting beams without the need to specify a velocity model. The analysis is performed in the time domain, which allows selecting a relatively narrow time window around the phase of interest while preserving frequency bandwidth. This technique is applied to earthquakes and hybrid events in the region of Fogo and Brava, two islands of the southern chain of the Cape Verde archipelago. The results show that the earthquakes mainly originate near Brava, whereas the hybrid events are located on Fogo. By multiple-event beam stacking we are able to further constrain the epicentral locations of the hybrid events in the northwestern part of the collapse scar of Fogo. In previous studies, these events were attributed to shallow hydrothermal processes. However, we obtain relatively high apparent velocities at the arrays, pointing to either deeper sources or complex ray paths. For a better understanding of possible errors of the multi-array analysis, we also compare slowness values obtained from the array analysis with those derived from earthquake locations from classical (local network) localizations. In general, the results agree well. Nevertheless, some systematic deviations of the array-derived back-azimuth and slowness values occur that can be quantified for certain event locations.

Natural Time Analysis of Global Seismicity

Natural time analysis enables the introduction of an order parameter for seismicity, which is just the variance of natural time χ, κ1=⟨χ2⟩−⟨χ⟩2. During the last years, there has been significant progress in the natural time analysis of seismicity. Milestones in this progress are the identification of clearly distiguishable minima of the fluctuations of the order parameter κ1 of seismicity both in the regional and global scale, the emergence of an interrelation between the time correlations of the earthquake (EQ) magnitude time series and these minima, and the introduction by Turcotte, Rundle and coworkers of EQ nowcasting. Here, we apply all these recent advances in the global seismicity by employing the Global Centroid Moment Tensor (GCMT) catalog. We show that the combination of the above three milestones may provide useful precursory information for the time of occurrence and epicenter location of strong EQs with M≥8.5 in GCMT. This can be achieved with high statistical significance (p-values of the order of 10−5), while the epicentral areas lie within a region covering only 4% of that investigated.

Spatio-temporal spread of COVID-19: Comparison of the inhomogeneous SEPIR model and data from South Carolina.

During the COVID-19 pandemic authorities have been striving to obtain reliable predictions for the spreading dynamics of the disease. We recently developed a multi-“sub-populations” (multi-compartments: susceptible, exposed, pre-symptomatic, infectious, recovered) model, that accounts for the spatial in-homogeneous spreading of the infection and shown, for a variety of examples, how the epidemic curves are highly sensitive to location of epicenters, non-uniform population density, and local restrictions. In the present work we test our model against real-life data from South Carolina during the period May 22 to July 22 (2020). During this period, minimal restrictions have been employed, which allowed us to assume that the local basic reproduction number is constant in time. We account for the non-uniform population density in South Carolina using data from NASA’s Socioeconomic Data and Applications Center (SEDAC), and predict the evolution of infection heat-maps during the studied period. Comparing the predicted heat-maps with those observed, we find high qualitative resemblance. Moreover, the Pearson’s correlation coefficient is relatively high thus validating our model against real-world data. We conclude that the model accounts for the major effects controlling spatial in-homogeneous spreading of the disease. Inclusion of additional sub-populations (compartments), in the spirit of several recently developed models for COVID-19, can be easily performed within our mathematical framework.

Worldwide Statistical Correlation of Eight Years of Swarm Satellite Data with M5.5+ Earthquakes: New Hints about the Preseismic Phenomena from Space

Nowadays, the possibility that medium-large earthquakes could produce some electromagnetic ionospheric disturbances during their preparatory phase is controversial in the scientific community. Some previous works using satellite data from DEMETER, Swarm and, recently, CSES provided several pieces of evidence supporting the existence of such precursory phenomena in terms of single case studies and statical analyses. In this work, we applied a Worldwide Statistical Correlation approach to M5.5+ shallow earthquakes using the first 8 years of Swarm (i.e., from November 2013 to November 2021) magnetic field and electron density signals in order to improve the significance of previous statistical studies and provide some new results on how earthquake features could influence ionospheric electromagnetic disturbances. We implemented new methodologies based on the hypothesis that the anticipation time of anomalies of larger earthquakes is usually longer than that of anomalies of smaller magnitude. We also considered the signal’s frequency to introduce a new identification criterion for the anomalies. We find that taking into account the frequency can improve the statistical significance (up to 25% for magnetic data and up to 100% for electron density). Furthermore, we noted that the frequency of the Swarm magnetic field signal of possible precursor anomalies seems to slightly increase as the earthquake is approaching. Finally, we checked a possible relationship between the frequency of the detected anomalies and earthquake features. The earthquake focal mechanism seems to have a low or null influence on the frequency of the detected anomalies, while the epicenter location appears to play an important role. In fact, land earthquakes are more likely to be preceded by slower (lower frequency) magnetic field signals, whereas sea seismic events show a higher probability of being preceded by faster (higher frequency) magnetic field signals.

Low-Frequency Marsquakes and Where to Find Them: Back Azimuth Determination Using a Polarization Analysis Approach

ABSTRACT National Aeronautics and Space Administration’s Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) mission on Mars continues to record seismic data over 3 yr after landing, and over a thousand marsquakes have been identified, to date. With only a single seismic station, the determination of the epicentral location is far more challenging than on the Earth. The Marsquake Service (MQS) produces seismicity catalogs from data collected by InSight, and provides distance and back azimuth estimates when these can be reliably determined; when both are available, these are combined to provide a location. Currently, MQS does not assign a back azimuth to the vast majority of marsquakes. In this work we develop and apply a polarization analysis method to determine the back azimuth of seismic events from the polarization of observed P- and S-wave arrivals. The method is first applied to synthetic marsquakes and then calibrated using a set of well-located earthquakes that have been recorded in Tennant Creek, Australia. We find that the back azimuth is estimated reliably using our polarization method. The same approach is then used for a set of high-quality marsquakes recorded up to October 2021. We are able to estimate back azimuths for 24 marsquakes, 16 of these without MQS back azimuths. We locate most events to the east of InSight, in the general region of Cerberus Fossae.

A new procedure for evaluating light-to-moderate earthquake location based on InSAR data and forward modeling tested on Mediterranean area

We propose a procedure based on remote sensing Sentinel-1 InSAR data aiming at evaluating the variability of the moment tensor solutions provided by different agencies in case of light-to-moderate earthquake. We model the expected coseismic ground deformations from the available moment tensor solutions and compare them with the real ones retrieved with the InSAR data. Any differences between location and intensity of simulated and estimated seismic-induced deformation fields allow indirectly evaluating the variability of the solutions in terms of epicenter locations and kinematics of the causative faults.We applied this investigation method to several light (4<Mw < 4.9) to moderate (5<Mw < 5.9) earthquakes occurred along the Mediterranean area since the launch of the Sentinel-1A mission in 2014. The selected seismic events cover all the faulting mechanisms and are characterized by different estimated magnitudes and depths thus offering a synoptic view of the performance of the procedure in several cases. Thanks to the global coverage and the unprecedented revisit time of Sentinel-1 acquisitions, the proposed procedure can be easily extended to any seismic event occurred inland worldwide.