Earthquake Fault Research Articles

A comparison of alternative curve fitting techniques for different earthquake fault parameters of Iranian earthquakes

In this study, we tried to estimate the optimum linear equations among the parameters associated with different earthquake fault mechanisms for Iranian earthquakes. For this purpose, we tested different curve fitting methods in order to present the most proper empirical relationships between several seismic parameters for different fault systems. In the present paper, 46 large and destructive Iranian earthquakes whose magnitudes change between 5.8 and 7.8 from 1900 to 2014 were used for the analyses. A comparison was made by using four types of curve fitting techniques. The estimation procedures are considered as (1) L2 or Least Squares Regression, (2) L1 or Least Sum of Absolute Deviations Regression, (3) Robust Regression and, (4) Orthogonal Regression. Confidence intervals were selected as 95% for all types of regression relationships. In the selection of the best probability distribution, we considered the correlation coefficients of the linear regressions as a powerful and conceptually simple method. Correlation coefficients of all relationships change between 0.299 and 0.986 with Orthogonal regression, between 0.168 and 0.792 with L1 regression, between 0.059 and 0.829 with Robust regression. For Iranian earthquakes, the most suitable and reliable empirical relationships between moment magnitude (Mw) and surface wave magnitude (Ms), Mw and surface rupture length (SRL), Mw and maximum displacement (MD), and SRL and MD were obtained by Orthogonal regression since it supplies stronger correlation coefficients than those of the other regression techniques in most estimates. The results show that estimated empirical relationships among the different fault parameters by using the Orthogonal regression method can be accepted as more up-to-date and more appropriate in comparison with the other regression norms. Consequently, these equations were suggested as more reliable in the estimation of the maximum surface displacement, maximum surface rupture length and associated with the maximum credible earthquakes for different areas of Iran. Furthermore, obtained relationships can be statistically significant for the assessment of seismic, tectonic and geologic activities, and they can be used to evaluate the rupture hazard of the Iranian Plateau.

Do intraplate and plate boundary fault systems evolve in a similar way with repeated slip events?

As repeated slip events occur on a fault, energy is partly dissipated through rock fracturing and frictional processes in the fault zone and partly radiated to the surface as seismic energy. Numerous field studies have shown that the core of intraplate faults is wider on average with increasing total displacement (and hence slip events). In this study we compile data on the fault core thickness, total displacement and internal structure (e.g., fault core composition, host rock juxtaposition, slip direction, fault type, and/or the number of fault core strands) of plate boundary faults to compare to intraplate faults (within the interior of tectonic plates). Fault core thickness data show that plate boundary faults are anomalously narrow by comparison to intraplate faults and that they remain narrow regardless of how much total displacement they have experienced or the local structure of the fault. By examining the scaling relations between seismic moment, average displacement and surface rupture length for plate boundary and intraplate fault ruptures, we find that for a given value of displacement in an individual earthquake, plate boundary fault earthquakes typically have a greater seismic moment (and hence earthquake magnitude) than intraplate events. We infer that narrow plate boundary faults do not process intact rock as much during seismic events as intraplate faults. Thus, plate boundary faults dissipate less energy than intraplate faults during earthquakes meaning that for a given value of average displacement, more energy is radiated to the surface manifested as higher magnitude earthquakes. By contrast, intraplate faults dissipate more energy and get wider as fault slip increases, generating complex zones of damage in the surrounding rock and propagating through linkage with neighbouring structures. The more complex the fault geometry, the more energy has to be consumed at depth during an earthquake and the less energy reaches the surface.

The Imbricated Foreshock and Aftershock Activities of the Balsorano (Italy) Mw 4.4 Normal Fault Earthquake and Implications for Earthquake Initiation

AbstractForeshocks in the form of microseismicity are among the most powerful tools to study the physical processes that occur before main earthquakes. However, their detection and precise characterization is still sparse, especially for small-to-moderate-size earthquakes (Mw<6). We present here a detailed foreshock analysis for the 7 November 2019, Balsorano, Italy, normal fault earthquake (Mw 4.4). To improve the detection of the microseismicity before and after the mainshock, we use six three-component broadband receivers at distances of less than 75 km from the targeted seismicity, through template matching. To improve the understanding of the physical mechanism(s) behind the earthquake initiation process, as well as other accompanying phenomena, we also detail the spatiotemporal evolution of the sequence associated with this medium-sized earthquake, using waveform clustering and hypocenter relocation. Clear differences between foreshocks and aftershocks are revealed by this analysis. Moreover, five distinct spatiotemporal patterns associated with the different seismic activities are revealed. The observed spatiotemporal behavior shown by the foreshocks highlights a complex initiation process, which apparently starts on an adjacent unmapped antithetic fault. Finally, the aftershock activity comprises four different clusters with distinct spatiotemporal patterns, which suggests that the different clusters in this sequence have distinct triggering mechanisms.

Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints

New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (Mw6.9) are integrated with a revision of pre-existing earthquake data and with an updated interpretation of the CROP-04 near-vertical seismic profile to reconstruct the surface and depth geometry, the kinematics and stress tensor of the seismogenic fault pattern. Three main fault alignments, organized in high-angle en-echelon segments of several kilometers in length, are identified and characterized. The inner and intermediate ones, i.e. Inner Irpinia (InIF) and Irpinia Faults (IF), dip eastward; the outer Antithetic Fault (AFA) dips westward. Both the InIF and the IF strike NW-SE along the northern and central segments and rotate to W-E along the southern segments for at least 16 km. We provide evidence of surface coseismic faulting (up to 1 m) not recognized before along the E-W segments and document coseismic ruptures with maximum vertical displacement up to ∼1 m where already surveyed from other investigators 40 years ago. Fault/slip data from surface data and a new compilation of focal mechanisms (1980 – 2018) were used for strain and stress analyses to show a coherent NNE-directed least principal stress over time and at different crustal depths, with a crustal-scale deviation from the classic SW-NE tensional direction across the Apennines of Italy. The continuation at depth of the outcropping faults is analyzed along the trace of the CROP-04 profile and with available hypocentral distributions. Integrating all information, a 3D seismotectonic model, extrapolated to the base of the seismogenic layer, is built. It outlines a graben-like structure with a southern E-W bend developed at depth shallower than 10–12 km, at the hanging wall of an extensional NE- to E-dipping extensional basal detachment. In our interpretation, such a configuration implies a control in the stress transfer during the 1980 earthquake ruptures and provides a new interpretation of the second sub-event, occurred at 20 s. Our reconstruction suggests that the latter ruptured a hanging wall NNE-dipping splay of the E-W striking main fault segment and possibly also an antithetic SSW-dipping splay, in two in-sequence episodes.

Creeping effect across a buried, inclined, finite strike-slip fault in an elastic-layer overlying an elastic half-space

The process of stress-strain accumulation near earthquake faults during the aseismic period has become a subject of research during the last few decades. It is noted that seismic waves, generated by an earthquake, result in a considerable disturbance in a seismic region causing a movement of the free surface. Such ground movements are not observed during the aseismic period. But a slow quasi-static aseismic surface displacement of the order of few cms. per year or less can be observed during the aseismic period which indicates a slow sub-surface process of stress-strain accumulation. Keeping this in view we here consider an aseismically creeping, buried, finite strike-slip fault inclined to the vertical at an arbitrary angle. The fault is situated in an elastic layer over an elastic half-space representing the lithosphere-asthenosphere system. An analytical study for displacement, stress and strain due to creeping effect has been carried out for a buried, finite, inclined fault. The solutions for displacement, stress and strain are then found before the onset of fault slip and then superpose the effect of fault slip using Laplace transform and suitable mathematical techniques of Green’s function. The analytical results and the graphical presentations show that the inclination of the fault and the velocities of the fault movement has noticeable effect on displacements, stresses and strains.

3D modeling of the ground deformation along the fault rupture and its impact on engineering structures: Insights from the 1999 Chi-Chi earthquake, Shigang District, Taiwan

The reactivation of the Chelungpu Fault triggered the 1999 Chi-Chi Mw 7.6 earthquake, resulting in substantial ground surface ruptures and severe damage. After the earthquake, the surveys organized by the Central Geology Survey (CGS) of Taiwan and the National Center for Research on Earthquake Engineering (NCREE) immediately investigated a variety of cases related to engineering structures damaged by substantial ground deformation. The investigations gathered valuable in-situ data before human activities disturbed the local setting and altered co-seismic features of interest, providing opportunities for studying the interaction between surface rupture and engineering structures. This study outlines the reconnaissance of damaged engineering structures in Shigang District that cover three typical types of foundations and analyzes the fault geometry and fault slip at the local scale to construct a geomechanical model for numerical simulation. In addition, 3-dimensional (3D) modeling was performed for each case study to investigate the damage mechanisms of the structures subjected to the substantial ground deformations by using PFC3D (Particle Flow Code 3D), which is based on the discrete element method (DEM). The results of the DEM analyses, which have been calibrated with the in-situ data, showed the ability to evaluate the overall ground deformation, the detection of structural movement, and the critical elements of progressive collapse during faulting. This study demonstrates that the 3D DEM simulation is a reliable analysis tool for studying earthquake fault rupture-overburden layer-engineering structure interactions and can produce useful information for hazard assessment with an acceptable computation time. The 3D DEM analysis is therefore suggested to be applied to assess the potential damage scenarios for the engineering structures located in active fault zones.

The 25 March 2020 MW 7.5 Paramushir, northern Kuril Islands earthquake and major (MW ≥ 7.0) near-trench intraplate compressional faulting

Large compressional-faulting earthquakes located relatively deep in oceanic lithosphere entering subduction zones are primarily caused by plate bending stress, but their timing, depth extent and size can be influenced by temporally-varying shear stress on the plate boundary. The 25 March 2020 MW 7.5 event in the Pacific plate seaward of Paramushir Island (northern Kuril Islands), is among the largest recorded events of this type. Its rupture extends along a large-slip region in the southwestern portion of the 1952 Kamchatka MW 9.0 rupture zone. This region has somewhat lower interplate coupling than the megathrust fault along Kamchatka to the northeast, but there could be 68 yrs of strain accumulation. The 2020 event is considered in the context of the 24 recorded major (MW≥7.0) near-trench intraplate compressional-faulting events. An updated compilation of temporally varying near-trench intraslab faulting relative to major interplate ruptures indicates that the stress cycles on the plate boundary influence both extensional and compressional near-trench faulting caused by plate bending. Particularly noteworthy are such events seaward of areas presumed to be in an advanced stage of their seismic cycle, including relatively shallow compressional events along the 1944 MW 8.1 Tonankai, Japan rupture zone, along with activity along the 1952 Kamchatka and 1922 Chile rupture zones.

Three dimensional seismic deformation-shear strain-swelling performance of America-California Oroville Earth-Fill Dam

Structural design of the vertical displacements and shear strains in the earth fill (EF) dams has great importance in the structural engineering problems. Moreover, far fault earthquakes have significant seismic effects on seismic damage performance of EF dams like the near fault earthquakes. For this reason, three dimensional (3D) earthquake damage performance of Oroville dam is assessed considering different far-fault ground motions in this study. Oroville Dam was built in United States of America-California and its height is 234.7 m (770 ft.). 3D model of Oroville dam is modelled using FLAC3D software based on finite difference approach. In order to represent interaction condition between discrete surfaces, special interface elements are used between dam body and foundation. Non-reflecting seismic boundary conditions (free field and quiet) are defined to the main surfaces of the dam for the nonlinear seismic analyses. 6 different far-fault ground motions are taken into account for the full reservoir condition of Oroville dam. According to nonlinear seismic analysis results, the effects of far-fault ground motions on the nonlinear seismic settlement and shear strain behaviour of Oroville EF dam are determined and evaluated in detail. It is clearly seen that far-fault earthquakes have very significant seismic effects on the settlement-shear strain behaviour of EF dams and these earthquakes create vital important seismic damages on the swelling behaviour of dam body surface. Moreover, it is proposed that far-fault ground motions should not be ignored while modelling EF dams.

Solar power plants site selection for sustainable ecological development in Nigde, Turkey

Turkey's population is constantly increasing, and thus, the energy consumption is also increasing. Wind turbines, nuclear power plants, and boron and uranium resources are used for energy needs. Turkey meets its energy needs using these resources. Sun which is a natural and unlimited resource among these resources is one of the most important natural energy resources. The most important issue to consider in order to utilize solar energy in the most efficient way and to obtain advantages is the selection of the suitable place for solar plants. The aim of this study is to select the most suitable location for solar energy plants and provide to build solar power plants in suitable places. Eleven data layers (sunshine duration, solar radiation, slope, aspect, road, water sources, residential areas, earthquake fault line, mine areas, power line and transformers) that were prepared using analytical hierarchy process (AHP) method in GIS were used and analysed. Based on the results of the analysis, the location of the areas where solar energy could be built was selected. As a result of the study, it was determined that in particular the north-east of the Nigde is the most suitable for solar plants. Ulukisla district has the most suitable feature for solar plants among the Nigde districts. 80% of the existing solar plants are located in the detected areas. It has been determined that the other 20% of the solar plant is also in the suitable areas, but their location is not suitable for the most efficiency.

Petrological and geochemical characteristics and deformation behavior of the Beichuan section of the Wenchuan Earthquake Fault Zone

Petrological and geochemical characteristics and deformation behavior of the Beichuan section of the Wenchuan Earthquake Fault Zone

ANALYSIS AND DESIGN OF MULTI-STOREY STEEL STRUCTURES ACCORDING TO DIFFERENT METHODS IN 2018 EARTHQUAKE REGULATIONS

Earthquake loads are the biggest obstacle to the design of multi-storey and irregular structures in countries located in the earthquake zone and with active earthquake faults. It is a dangerous natural disaster that can result in loss of life and property depending on the intensity of the earthquake. It is important to use comprehensive and up-to-date standards and regulations for the calculation of earthquake loads. In this study, considering TBDY-2018, dynamic behavior of multi-storey steel structure with irregularity called A1 Torsional Irregularity has been investigated. For seismic load calculations, mode combination method and equivalent earthquake load method, which are linear analysis methods, were used. In a 10-storey steel structure, central inverted V braces were used and the positions of these braces were changed and a total of 4 models were produced. Structural analyzes were made using the "Etabs" program. Then, the results obtained in the two methods used were compared, and in the structural analysis of the models used, it was seen that the internal forces and displacements gave greater results when the calculations were made with the Equivalent Earthquake Load Method. In addition, it has been stated that the torsional irregularity coefficient of the structure is effective in the horizontal displacement of the structure.

Identification of paddy fields using temporal NDVI changes in Minamiaso Village, Kumamoto Prefecture, Japan to estimate groundwater recharge

In Minamiaso Village (Kumamoto Prefecture, Japan), land covers of forests, grasslands, and paddy fields play an important role in groundwater recharge. The land covers have been changed in a past few decades by agricultural systems and natural disasters: landslides, slope failures, and damage of irrigation canals caused by the 2016 Kumamoto earthquake in Japan. In this study, we extracted training data for classifying the land covers, and detected the temporal change of NDVI (Normalized Difference Vegetation Index) for each land cover. To quantify the impact of past land cover change on the groundwater recharge, we need to grasp the area of each land cover with the different hydrological parameters such as infiltration capacities. In the case of paddy fields, its distribution also should be known because the infiltration rates that we investigated vary depending on the paddy fields. We attempted to identify the paddy field distribution by the obtained NDVI values, and confirmed that the paddy field areas near the earthquake faults damaged by the earthquake where are still not usable were well distinguished. The paddy field distribution based on NDVI was almost matched with that based on SAR.

Сейсмичность юга Дальнего Востока России в 2020 году

The paper presents an overview of the seismicity of the southern part of the Russian Far East for 2020: the Amur–Primorye region, Sakhalin and Kuril-Okhotsk regions. It is based on the preliminary data from the earthquake catalogs of the Sakhalin Branch of the Federal Research Center “United Geophysical Survey of the Russian Academy of Sciences” (SB FRC UGS RAS). An analysis of the seismicity of the regions for 2020 in comparison with the previous decade is performed. Information about the earthquakes of 2020, which are the most significant and worthy of separate study, is given. These events occurred in the SB FRC UGS RAS responsibility zone: an earthquake near the Zeyskaya HPP, a deep-focus earthquake in the Tatar Strait, an earthquake at intermediate depths in the Southern Kuril Islands, a reverse fault earthquake on the bend of the Pacific lithospheric plate in the Northern Kuril Islands. According to formal indicators, the seismicity of the regions in 2020 remained within the background values, but it approached the upper limit of their range in the Kuril-Okhotsk region and in the mantle under the territory of the Sakhalin region.

Stress Promotion of the 1958 Mw∼7.8 Fairweather Fault Earthquake and Others in Southeast Alaska by Glacial Isostatic Adjustment and Inter‐earthquake Stress Transfer

AbstractWe assess how recent glacial isostatic adjustment (GIA) and inter‐earthquake stress transfer modulated the state of stress on major faults in Southeast Alaska, and how these effects may have influenced recent large and moderate earthquakes. The Glacier Bay Icefield has lost >3,000 km3 of ice since ca. 1770, with ice thinning up to 1.5 km, and the rest of southeast Alaska has been deglaciating since ca. 1900. The resulting GIA response in the solid earth produces present‐day surface uplift rates of up to ∼4 cm/yr, among the fastest on Earth. This rapid deformation occurs directly alongside and atop the Fairweather Fault, which accommodates 4–5 cm/yr of right‐lateral motion through slip in frequent large earthquakes, recently including a Mw∼7.8 earthquake in 1958. We find that the 1958 earthquake nucleated very close to the location of maximum GIA‐induced Coulomb stress increase on the Fairweather Fault between 1770 and 1958 (estimated at ∼0.2–0.6 MPa), on the only section of fault where GIA‐induced stress changes had involved both right‐lateral shearing and unclamping. The September 10, 1899 Mw∼8.1 Yakutat Bay earthquake also promoted failure on at least the northwest part of the eventual 1958 rupture. In turn, the 1899 and 1958 earthquakes and GIA promoted failure along the St. Elias compressional margin, the site of a Mw∼7.4 event in 1979. While rapid tectonic loading is very likely the main driver of earthquakes in southeast Alaska, we estimate that 23 of 30 instrumentally constrained Mw ≥ 5.0 earthquakes in this region were also promoted by post‐1770 GIA.

Analysis of Tsunami Inundation due in Pangandaran Tsunami Earthquake in South Java Area Based on Finite Faults Solutions Model

On July 17, 2006 an earthquake with a magnitude of 7.7 triggered a tsunami that struck 500 km of the coast in the south of the island of Java. The tsunami generated is classified as an earthquake tsunami because the waves generated were quite large compared to the strength of the earthquake. The difference in the strength of the earthquake and the resulting tsunami requires a tsunami modeling study with an estimated fault area in addition to using aftershock and scaling law. The purpose of this study is to validate tsunamis that occur based on the estimation of the source mechanism and the area of earthquake faults. Determination of earthquake source mechanism parameters using the Teleseismic Body-Wave Inversion method that uses teleseismic waveforms with the distance recorded waveform from the source between Whereas, tsunami modeling is carried out using the Community Model Interface for Tsunami (commit) method. Fault plane parameters that obtained were strike , dip , and rake with dominant slip pointing up to north-north-west with a maximum value of 1.7 m. The fault plane is estimated to have a length of 280 km in the strike direction and a width of 102 km in the dip direction. From the results of the tsunami modeling, the maximum inundation area is 0.32 km2 in residential areas flanked by Pangandaran bays and the maximum run-up of 380.96 cm in Pasir Putih beach area. The tsunami modeling results in much smaller inundation and run-up from field observations, it was assumed that the fault plane segmentation had occurred due to the greater energy released than the one from the fault area, causing waves much larger than the modeling results.

NEAR-FIELD TSUNAMI FORECASTING BASED ON A TSUNAMI RUN-UP RESPONSE FUNCTION

Since near-field-generated tsunamis can arrive within a few minutes to coastal communities and cause immense damage to life and property, tsunami forecasting systems should provide not only accurate but also rapid tsunami run-up estimates. For this reason, most of the tsunami forecasting systems rely on pre-computed databases, which can forecast tsunamis rapidly by selecting the most closely matched scenario from the databases. However, earthquakes not included in the database can occur, and the resulting error in the tsunami forecast may be large for these earthquakes. In this study, we present a new method that can forecast near-field tsunami run-up estimates for any combination of earthquake fault parameters on a real topography in near real-time, hereafter called the Tsunami Run-up Response Function (TRRF).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/tw1D29dDxmY

Numerical analysis of interseismic, coseismic and post-seismic phases for normal and reverse faulting earthquakes in Italy

SUMMARYThe preparation, initiation and occurrence dynamics of earthquakes in Italy are governed by several frequently unknown physical mechanisms and parameters. Understanding these mechanisms is crucial for developing new techniques and approaches for earthquake monitoring and hazard assessments. Here, we develop a first-order numerical model simulating quasi-static crustal interseismic loading, coseismic brittle episodic dislocation and post-seismic relaxation for extensional and compressional earthquakes in Italy based on a common framework of lithostatic and tectonic forces. Our model includes an upper crust, where the fault is locked, and a deep crust, where the fault experiences steady shear.The results indicate that during the interseismic phase, the contrasting behaviour between the upper locked fault segment and lower creeping fault segment generates a stretched volume at depth in the hangingwall via extensional tectonics while a contracted volume forms via compressional tectonics. The interseismic stress and strain gradients invert at the coseismic stage, with the interseismic dilated volume contracting during the coseismic stage, and vice versa. Moreover, interseismic stress gradients promote coseismic gravitational subsidence of the hangingwall for normal fault earthquakes and elastic uplift for reverse fault earthquakes. Finally, the post-seismic relaxation is characterized by further ground subsidence and uplift for normal and reverse faulting earthquakes, respectively, which is consistent with the faulting style. The fault is the passive feature, with slipping generating the seismic waves, whereas the energy activating the movement is stored mostly in the hangingwall volume. The main source of energy for normal faulting and thrust is provided by the lithostatic load and elastic load, respectively.

Seismicity in the Gulf of California, Mexico, in the period 1901–2018

We compile a new catalog of earthquakes that occurred in the region of the Gulf of California, Mexico, between 1901 and 2018. We include events reported by the catalog of the seismic network RESNOM (Red Sísmica del Noroeste de México) operated by the CICESE (Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California) and complemented with events listed in the ISC (International Seismological Centre) and the SSN (Servicio Sismológico Nacional, UNAM) catalogs. The minimum magnitude of completeness of this catalog is Mc = 3.6, and we find that many hypocenters concentrate between 5 km and 10 km depth, the likely depth of the seismogenic zone of the earthquakes in the Gulf of California. We identify active and inactive faults in this region, and we detected faults located approximately 300 km SE of April 2010 El Mayor-Cucapah (Mw 7.2) earthquake that were probably reactivated by this earthquake sequence. We additionally compiled a catalog of focal mechanisms and found that most strike-slip fault earthquakes are located on transform faults and normal fault earthquakes near the spreading centers. We also detected seismicity lineaments and strike-slip events off the major transform faults that tend to occur parallel to the ridge direction either at the continental crust or at the oceanic-continental transition zone as previously reported by Ortega and Quintanar (2010) in the southern gulf.

Short Review on Soil-Structure Implementation in Base Isolated Structures

Structural control is a subject that has been gaining interest for almost the last forty years. However, soil-structure interaction (SSI) implementation in control studies is relatively new, but it has attracted many researchers’ attention for both theoretical and experimental research. Besides structural control SSI is an important topic which should be studied more. SSI was not considered during the design stages of different structures, which led in the unexpected results after the earthquakes. In this paper the studies considering SSI in base isolated structures are reviewed. From the structural and earthquake engineering point of view, many studies considered near or far fault earthquakes and used scaled mathematical models for numerical examples. Most of the research is based on existing results of the earthquakes and real building damages. On the other hand, there are some researchers who designed scaled structures to perform experimental works under artificial earthquake excitation in order to investigate the seismic performance of the structures. This study aims to demonstrate the conclusion and numerical examples obtained from base isolation studies considering SSI. With regards to the short review, it can be mentioned that SSI affects the structure and the behaviour of the base isolation. Considering SSI in base isolation research might increase the authenticity of the corresponding study and might result in more realistic results than fixed base structural analysis.

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the Mw 6.9 Zakynthos Earthquake, Greece

AbstractThe month‐to‐year‐long deformation of the Earth's crust where active subduction zones terminate is poorly explored. Here we report on a multidisciplinary data set that captures the synergy of slow‐slip events, earthquake swarms and fault interactions during the ∼5 years leading up to the 2018 Mw 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). It appears that this long‐lasting preparatory phase initiated due to a slow‐slip event that lasted ∼4 months and released strain equivalent to a ∼Mw 6.3 earthquake. We propose that the slow‐slip event, which is the first to be reported in the HSS, tectonically destabilized the upper 20–40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (Mw < 4) on neighboring faults, earthquake swarms in the epicentral area of the Mw 6.9 earthquake ∼1.5 years before the main event, another episode of slow slip immediately preceding the mainshock and, eventually, the large (Mw 6.9) Zakynthos Earthquake. Tectonic instability in the area is evidenced by a prolonged (∼4 years) period of overall suppressed b‐values (<1) and strong earthquake interactions on discrete strike‐slip, thrust and normal faults. We propose that composite faulting patterns accompanied by alternating (seismic/aseismic) deformation styles may characterize multifault subduction‐termination zones and may operate over a range of timescales (from individual earthquakes to millions of years).