Large Coseismic Slip Research Articles

Localization of Deformation on Faults Driven by Fluids During the L’Aquila 2009 Earthquake

AbstractCoseismic rupture and aftershock development on a fault plane are complex and heterogeneous processes. The Mw 6.1 L’Aquila 2009 normal faulting earthquake is a perfect case to explore how fault geometry and rheology influence the rupture process and aftershocks distribution. In this study, we use for the first time a dense set of earthquake data to obtain enhanced images of the causative normal fault structure to the kilometer scale. The hypocenter of the emergent onset of the mainshock took place within a low Vp/Vs volume, while the large coseismic slip occurred a few kilometers above, as the rupture propagated through a high Vp and high Vp/Vs fluid‐filled rock volume. The increase of Vp/Vs in the fault hanging wall during the sequence suggests a strong dehydration in the earthquake asperity, with an upward fluid pressure migration along the fault toward the host rock volume. We propose that the localization of deformation on the fault plane is favored by high fluid pressure, while the spreading of aftershocks on a wide volume around the fault is driven by the depletion of fluids from the slipped portion of the fault plane and migration to small segments within the fault host rocks.

Background and clustering characteristics of recent seismicity in Southwestern China

SUMMARY This study analysed seismicity in southwestern China (1 January 2008 to 30 June 2021) using the earthquake catalogue compiled by the China Earthquake Network Center and four different space–time Epidemic-Type Aftershock Sequence models: the 2-D point-source (PS) model, the 2-D finite-source (FS) model, the 3-D PS model and the 3-D FS model. Our objective was to understand the features of the background seismicity and the patterns of earthquake clusters to better evaluate the regional seismic hazard. We carefully investigated the aftershock sequences that followed 7 of the 10 MS ≥ 6.0 earthquakes that have struck this region since the occurrence of the 2008 Wenchuan MS 8.0 earthquake [i.e. the Panzhihua (31 August 2008; MS 6.0), Yaoan (9 July 2009; MS 6.0), Lushan (20 April 2013; MS 7.0), Ludian (3 August 2014; MS 6.5), Jinggu (7 October 2014; MS 6.6), Kangding (11 November 2014; MS 6.3) and Yangbi (21 May 2021; MS 6.4) earthquakes]. Our results revealed the following. (1) The background seismicity level for natural earthquakes is usually stable but can experience sudden change due to major events, such as the 2014 Ludian MS 6.5, and the 2014 Jinggu MS 6.6 events. Such changes in the background rate can reach 50 per cent. (2) Reservoir-induced earthquakes substantially increase the level of regional seismicity, indicating that they cannot be ignored when analysing natural seismicity and evaluating regional earthquake hazards. (3) Events triggered directly by the main shock occur mostly in regions adjacent to areas with large coseismic slip, showing a pattern complementary to the main shock ruptures.

Unraveling the roles of fault asperities over earthquake cycles

Fault asperities can produce concentrated slips during large earthquakes and intensify damage. However, how asperities control fault behavior during other phases of the earthquake cycle remains poorly known. Here, we conduct friction experiment on a laboratory fault featuring two prominent geometric asperities to directly image their influences on long-term and short-term seismicity, and the nucleation and propagation of the mainshock. The laboratory observations and supporting numerical simulations reveal that one asperity located in the fault interior behaves firstly as a mechanical attractor to long-term seismicity, then a barrier to preseismic slow slip, and ultimately a source of large coseismic slip. In contrast, another asperity located near the fault margin primarily undergoes persistent aseismic slip throughout most phases of the earthquake cycle. These results provide new insights into how asperities partition strain across a broad spatiotemporal domain, establishing a physical link between long-term and short-term fault behaviors and the occurrence of large earthquakes.

Aftershocks following the 2011 Tohoku-Oki earthquake driven by both stress transfer and afterslip

Aftershocks are a fundamental characteristic of seismicity, and their generation mechanism is mainly characterized by two physical models, stress transfer from large earthquakes and afterslip-induced stress loading. However, the contribution of each mechanism to aftershock generation remains unclear. Here we investigate the spatiotemporal variations in aftershock activity following the 2011 Tohoku-Oki earthquake by applying the Hierarchical Space–Time Epidemic-Type Aftershock Sequence (HIST-ETAS) model to the decade of recorded seismicity since the mainshock. Using the estimated HIST-ETAS model, we categorize the aftershocks into background earthquakes (which are caused by aseismic phenomena) and triggered earthquakes (which are caused by earthquake-to-earthquake interactions). Most of the earthquakes that occurred updip of the large coseismic slip zone along the Japan Trench are triggered earthquakes, consistent with the lack of afterslip in this area. Conversely, background earthquakes are the predominant earthquake type in the long-term downdip of the large coseismic slip zone, and they positively correlate with the afterslip evolution. Our results suggest the importance of combining these two end-member aftershock generation models to explain aftershock activity and thus provide new insights into the relationship between afterslip and spatiotemporal aftershock distribution. Our classifications may also contribute to the monitoring of afterslip in a given region that hosts a large earthquake, particularly where geodetic observation networks are too sparse to evaluate afterslip evolution.

The 2022 Mw 6.7 Menyuan Earthquake on the Northeastern Margin of the Tibetan Plateau, China: Complex Surface Ruptures and Large Slip

ABSTRACT On 8 January 2022, the Mw 6.7 Menyuan earthquake occurred near the stepover of the Lenglongling (LLLF) and Tuolaishan (TLSF) faults of the Qilian–Haiyuan fault zone in the middle of the northeastern Tibetan plateau. Field investigations and unmanned aerial vehicle-based photogrammetry revealed that the earthquake generated five surface rupture zones with different strikes and kinematic properties. Two large rupture zones, R1 (∼22.8 km long) and R2 (∼3.9 km long), occurred along the northern branch of the western LLLF and the eastern segment of TLSF, respectively, and featured left-lateral strike slips. Among the three small rupture zones, the left-lateral strike-slip-type R3 (0.6 km long) was located in the extension direction of R2, whereas the thrust-type R4 (∼3.3 km long) and R5 (∼1.1 km long) zones were located north of the central section of R1. These complex multifault ruptures were caused mainly by the rupture of strike-slip faults on both sides of the stepover structure. A small amount of compressive shortening strain was released during the earthquake due to regional oblique compression. The total length of the rupture zone was ∼31.7 km; the maximum left-lateral and vertical offsets were 3.5 ± 0.3 and 0.47 ± 0.04 m, respectively. Compared with the relationship observed between coseismic slips and magnitudes in historical and modern earthquakes in western China, the 2022 Menyuan earthquake produced a large coseismic slip in relation to its magnitude. The distribution characteristics of the aftershock belts and their relationship with rupture zones showed that the seismogenic fault of the earthquake was nearly east–west-striking TLSF, which may have triggered the rupture of the northern branch of the western LLLF. In addition, only a small segment of TLSF was ruptured, indicating that the accumulated strain could not be released completely during the earthquake and that this remains the most likely area for the occurrence of large earthquakes in the future.

Large extensional earthquakes push-up terrific amount of fluids

How large earthquakes are triggered is a key question in Earth science, and the role played by fluid pressure seems to be crucial. Nevertheless, evaluation of involved fluid volumes is seldom investigated, if not unaccounted for. Moreover, fluid flow along fault zones is a driving factor for seismicity migration, episodic heat and chemical transport. Here we show that time repeated (4D) seismic tomography resolves changes of Vp and Vp/Vs during the Mw6.2 2009 L’Aquila normal faulting sequence, that indicate a post-failure fluid migration from hypocentral depths to the surface, with a volume estimated between 5 and 100 × 106 m3 rising at rates up to 100 m/day. This amount inferred by tomograms is surprisingly consistent with the about 50 × 106 m3 surplus water volume additionally measured at spring discharge, spread in time and space along the 700 km2-wide regional carbonate fractured aquifer. Fluids were pushed-up within a huge volume across the fault and expelled from the area of large coseismic slip. Such quantities of fluids liberated during earthquakes add unprecedented constraints to the discussion on the role of fluids during and possibly before earthquake, as well as to the potential impact on the pristine high-quality drinkable groundwater, possibly affecting the biodiversity of groundwater dependent ecosystems too.

Seismicity distribution in the Tonankai and Nankai seismogenic zones and its spatiotemporal relationship with interplate coupling and slow earthquakes

We conducted seismic tomography to estimate the seismic velocity structure and to evaluate the spatiotemporal distribution of interplate earthquakes of the Kii Peninsula, central Honshu, Japan, where the Tonankai and Nankai megathrusts are located. Microearthquakes were quantitatively detected by using the data from a cable-type seafloor seismic observation network, completed in 2015. Our velocity model was consistent with the previous 2-D active-source surveys, which reported the areal extent of key structures: a high-velocity zone beneath Cape Shionomisaki, a subducted seamount off Cape Muroto, and the subducted Paleo-Zenith Ridge. The absence of any other subducted seamount with the same or larger spatial scale, than the identified key structures, was confirmed. Our velocity model also revealed that there was not a simple relationship between areas of large coseismic slip or strong interplate coupling and areas of high velocity in the overriding plate. Relocated hypocenters widely ranged from the upper plate to within the slab, while the most active region was attributed to the oceanic crust in the aftershock region of 2004 off-Kii earthquake. Compared with the results from the land-based observation network, the accuracy of the focal depth estimation was substantially improved. Furthermore, we identified the seismic activity in the vicinity of the plate boundary and determined 14 locations for interplate seismicity areas. They were primarily distributed in the range of seismogenic zone temperature (150–350 °C) along the plate boundary and were located outside of the strong interplate coupling zone. Several active areas of interplate earthquakes exhibited clustered activity during the periods of slow-slip events, observed and accompanied with shallow very-low-frequency earthquakes. Thus, regular interplate microearthquakes became active at the plate boundary in the conjunction with slow slip. In summary, as regular earthquakes provide a more accurate source location than slow earthquakes and can detect events of smaller magnitude, monitoring such interplate earthquakes may reveal spatiotemporal variations in the stick–slip conditions on the plate boundary.

Structural Anomaly at the Boundary Between Strong and Weak Plate Coupling in the Central‐Western Nankai Trough

AbstractTo investigate structural characteristics associated with variations in slip behavior on the plate boundary in the Nankai subduction zone, we conducted seismic reflection surveys in the central‐western Nankai Trough. Data were processed by pre‐stack depth migration. The resulting depth map of the top of the subducting Philippine Sea plate shows detailed topographic features of the plate boundary, including subducting seamounts and large‐scale undulations of the plate surface. We report the presence of a structurally anomalous region, potentially with low velocity, in the overriding plate at the boundary between the zone of large coseismic slip during the 1946 Nankai earthquake and the area producing slow earthquakes. This anomaly appears to be related to depth‐dependent variations in plate boundary slip style and plate coupling in the central‐western Nankai Trough.

The 2020Mw 6.4 Petrinja earthquake: a dextral event with large coseismic slip highlights a complex fault system in northwestern Croatia

SUMMARYOn 2020 December 29, the Mw 6.4 Petrinja earthquake hit the Kupa Valley region and set a record for the largest earthquake in northwestern (NW) Croatia. The coseismic surface displacements are well obtained on three pairs of interferometric synthetic aperture radar images from Sentinel-1 satellites. The interferograms exhibit coseismic ground deformation with a maximum line-of-sight displacement of 0.4 m. Based on the coseismic deformation field, we investigate both the fault geometry and the coseismic slip distribution. The results show a dextral event with a peak slip of 3.50 m at a depth of 3.47 km. The shallow depth and unusually large coseismic slip correspond to obvious ground deformation and serious damage in the epicentral zone. The 2020 earthquake highlights an unmapped, steeply dipping strike-slip fault, which possibly enabled a potential ‘curve cut-off’ process on the bending segment of the Pokupsko fault in the context of ∼N–S compression in NW Croatia. The large coseismic slip and high stress drop associated with the Mw 6.4 Petrinja earthquake are likely products of the geometrically complex fault zones and immature seismotectonic environment in NW Croatia.

Presence of interplate channel layer controls of slip during and after the 2011 Tohoku-Oki earthquake through the frictional characteristics

There are significant differences between the middle and southern segments of the Japan Trench in terms of the seismic and aseismic slips on the plate interface and seismic velocity structures. Although the large coseismic slip of the 2011 Tohoku-Oki earthquake was limited to the middle segment, the observed negative residual gravity anomaly area in the southern segment corresponds to the postseismic slip area of the Tohoku-Oki earthquake. A density distribution model can explain the different slip behaviours of the two segments by considering their structural differences. The model indicates that the plate interface in the south was covered with a thick channel layer, as indicated by seismic survey imaging, and this layer resulted in a residual gravity anomaly. Numerical simulations which assumed evident frictional heterogeneity caused by the layer in the south efficiently reproduced M9 earthquakes recurring only in the middle, followed by evident postseismic slips in the south. This study proposes that although the layer makes the megathrust less compliant to seismic slip, it promotes aseismic slips following the growth of seismic slips on the fault in an adjacent region.

Locking-derived tsunami scenarios for the most recent megathrust earthquakes in Chile: implications for tsunami hazard assessment

The ever-increasing data from continues geodetic networks has allowed to reveal first-order spatial relations between pre-seismic highly locked zones on the interface and regions of large coseismic slip. Here we use a distribution of locking degree and recurrence of historical earthquakes along the Chilean subduction zone to estimate the slip deficit accumulated since previous tsunamigenic earthquakes and use these constrains to simulate tsumani signals. We generate tsunami models for the recent five major tsunamigenic earthquakes in Chile during the last decade: Maule (2010), Pisagua (2014), Illapel (2015), Melinka (2016) and Valparaiso (2017). Results were compared with tsunami records to evaluate the use of locking degree as an estimate of displacement of future earthquakes and as a tool for tsunami hazard assessment. Our tsunami simulations for the Maule (2010) and Illapel (2015), earthquakes that filled a seismic gap, reproduce well the tsunami observations, for the case of Pisagua (2014), Valparaiso (2016) and Melinka (2017) although it exists a correspondence in the areas of greater degree of locking with the coseismic slip, there is also an imbalance between the energy accumulated and released in the interseismic period considered according to the historical seismicity. This indicate that the rupture of small asperities (areas that release high slip during earthquakes) may have a complex pattern of recurrence and do not fully affect a locked patch. Locking-derived tsunami scenarios represent well tsunami observations of earthquakes that ruptured a locked seismic gap, and they can be used in addition to the actual methodologies to improve the estimation of tsunami hazard.

Basal Accretion Along the South Central Chilean Margin and Its Relationship to Great Earthquakes

AbstractThe south central Chilean margin regularly produces many of the world's largest earthquakes and tsunami, including the 2010 Mw 8.8 Maule and 1960 Mw 9.5 Valdivia events. In 2017, we acquired seismic reflection data along ~1,000 km of the margin using the R/V Langseth's 15 km long receiver array and 108.2 l (6,600 in3) seismic source to image structures associated with these ruptures. We focus on the Valdivia segment with the largest coseismic slip (~40 m). The outer 40 km of the forearc is an accretionary wedge constructed primarily of stacked sedimentary packages with irregular lengths and thicknesses and little along‐strike continuity. Forearc structures indicate that the accretionary wedge grows primarily through basal accretion of the downgoing trench fill. The décollement propagates along a weak boundary near the top of the trench fill but occasionally branches downward into the underthrust sediment along bedding horizons, peeling off slices that are underplated to the forearc. The shallow décollement level and the rarity of underplating events allow most of the trench sediment to subduct. As a result, only ~30% of the incoming sediment has been accreted since the Early Pliocene. This implies that, on average, ~1 km of sediment must subduct beyond the outer forearc, an inference that is supported by our seismic images. We propose that the thickness and great downdip and along‐strike extent of the underthrust layer, which separates the megathrust from the underlying roughness of the igneous ocean crust, ensures a smooth broad zone of strong coupling that generates the world's largest earthquakes and tsunami.

Spatio-temporal foreshock evolution of the 2019 M 6.4 and M 7.1 Ridgecrest, California earthquakes

The 2019 M 6.4 and M 7.1 Ridgecrest, California earthquake sequence provides an ideal opportunity to study the seismicity evolution and interaction among multiple complex fault structures. Here, we apply the matched-filter detection method to obtain a relatively complete (magnitude of completeness ≈ 0.9) and precisely relocated earthquake catalog. The results show a short-duration (∼ 31 minutes) foreshock sequence with 28 events, before the M 6.4 earthquake. The foreshock sequence started with a M 4.0 event and was aligned along the NW-SE direction. This implies that the M 6.4 rupture initiated on a NW trending fault segment, before rupturing the primary SW trending fault. Repeating earthquakes before and after the M 7.1 event are separated in space and bound the areas of large coseismic slip in the M 6.4 and M 7.1 events. This might reflect local slow slip acceleration near the edges of coseismic rupture asperities. The NW-striking fault zones illuminated by seismicity are separated into several sub-regions with distinct pre-M7.1 seismicity rate evolutions. The M 7.1 event nucleated in a region of local seismicity concentration which intensified ∼ 3 hr before the M 7.1 mainshock. The M 7.1 nucleation zone is characterized by a significantly low b value of events that occurred since the M 6.4 event, which might indicate local failure conditions approaching a critical state.

Stress Field Variation During the 2019 Ridgecrest Earthquake Sequence

AbstractWe investigate the spatiotemporal variations of the stress field and the deviatoric stress associated with the 2019 Ridgecrest earthquake sequence using the USGS earthquake focal mechanisms. We find that while the M 6.4 foreshock causes no notable stress changes, the stress field adjustment due to the M 7.1 mainshock exhibits significant spatial complexities. The area of large stress change is generally correlated with the fault segments with large coseismic slip. Although there are no resolvable stress changes at the two terminal ends of the mainshock, the mainshock produces a ~5° clockwise rotation of the maximum horizontal stress (SHmax) near the M 6.4 foreshock epicenter. The inferred deviatoric stress is approximately 8.0 MPa, almost equivalent to the coseismic stress drop of 7.4 MPa in its epicenter area. Such nearly complete stress release is supported by the postseismic stress heterogeneity near the mainshock epicenter.

Stress drop assessment of the August 8, 2017, Jiuzhaigou earthquake sequence and its tectonic implications*

By using a broadband Lg attenuation model developed for the Tibetan Plateau, we isolate source terms by removing attenuation and site effects from the observed Lg-wave displacement spectra of the M7.0 earthquake that occurred on August 8, 2017, in Jiuzhaigou, China, and its aftershock sequence. Thus, the source parameters, including the scalar seismic moment, corner frequency and stress drop, of these events can be further estimated. The estimated stress drops vary from 47.1 kPa to 7149.6 kPa, with a median value of 59.4 kPa and most values falling between 50 kPa and 75 kPa. The estimated stress drops show significant spatial variations. Lower stress drops were mainly found close to the mainshock and on the seismogenic fault plane with large coseismic slip. In contrast, the highest stress drop was 7.1 MPa for the mainshock, and relatively large stress drops were also found for aftershocks away from the major seismogenic fault and at depths deeper than the zone with large coseismic slip. By using a statistical method, we found self-similarity among some of the aftershocks with a nearly constant stress drop. In contrast, the stress drop increased with the seismic moment for other aftershocks. The amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process. As such, the stress drop represents a key parameter for improving our understanding of earthquake source physics.

Detecting Offshore Seismicity: Combining Backprojection Imaging and Matched‐Filter Detection

AbstractAn important manifestation of the background or coseismic deformation surrounding megathrust earthquakes is the offshore microseismicity, which are difficult to be directly detected by land‐based seismic instruments. Here, we improve the capability of detecting offshore events by combining two popular techniques: backprojection (BP) imaging and matched‐filter (MF) detection. The BP method is effective in retrieving offshore seismicity (Mw > 4.5) buried in the coda wave of large earthquakes. The capability of the MF method depends on the availability of the template pool; therefore, the BP‐inferred events can be used as additional templates to expand the MF detections (BP‐MF). We performed the BP‐MF approach in the period within 600 days after the 2011 Mw 9.0 Tohoku earthquake. We find overall 44.2% more offshore events than those listed in the Japan Meteorological Agency (JMA) catalog. In the near‐trench area, we detect 213% more events. Among the newly detected Mw > 4 events, the BP template contributions are twice more than those matched by the JMA templates. Based on the spatial consistency between aftershock‐depleted zones and large coseismic slip, we identify a possible large coseismic slip zone in the near‐trench region offshore Fukushima. Large b values (≥1.2) are found close to large aftershocks, possibly indicating localized pockets of small differential stresses. At several locations close to the trench, p values (0.93–1.11) are higher than those in the inland area (0.64–0.85). This may be due to the larger coseismic slip and hence larger stress drop of the outer‐rise normal‐faulting events compared to the deeper thrust‐faulting events.

Correlation of frontal prism structures and slope failures near the trench axis with shallow megathrust slip at the Japan Trench

Since the giant 2011 Tohoku earthquake and tsunami, much research has focused on the distribution of coseismic slip at shallow depths during this subduction megathrust event. Here we present seismic images obtained in the immediate vicinity of the trench axis, that show thrust faults and fold-and-thrust type deformation structures near the epicenter of the 2011 Tohoku earthquake where the large coseismic slip has been inferred, and chaotic structure and the absence of thrust faults in northern and southern source areas. Seismic profiles show evidence of slope failures of the trench inner wall in a proposed tsunami source region around 39°–40° N, where the slips estimated from previous studies are in disagreement. Our results show that structural characteristics in the trench axis may be related to the occurrence of shallow megathrust slip and tsunamigenesis in the Japan Trench.

Large Coseismic Slip to the Trench During the 2011 Tohoku-Oki Earthquake

The strong ground motions, large crustal deformation, and tsunami generated by the 2011 Tohoku-oki earthquake ( Mw 9.1) reveal that a large coseismic slip likely propagated to shallow depth in the Japan Trench. Although data acquired by onshore networks cannot resolve the slip behavior of the updip fault rupture, marine geophysical and geological studies provide direct evidence of coseismic slip to the trench. Differential bathymetry data show ∼50 m of coseismic seafloor displacement extending to the central Japan Trench (38–39.2°N). Seismic data show that coseismic slip ruptured the seafloor within the trench. Pelagic clays may have promoted slip propagation to shallow depths, whereas disturbed/metamorphosed clays may have restricted slip to the main rupture zone. Those observations imply that a smooth, broadly distributed, weak, clay-rich sediment in a shallow part of a subduction zone is a characteristic factor that can foster a large coseismic slip to the trench and, consequently, the generation of a large tsunami. ▪ During the 2011 Tohoku-oki earthquake ( Mw 9.1), more than ∼50 m of slip occurred on a fault that ruptured the seafloor in the central Japan Trench. ▪ The fault rupture reaching the seafloor caused a large tsunami. ▪ Marine geophysical explorations revealed that a clay-rich sediment in the subduction zone was one factor fostering the large fault slip. ▪ Understanding of slip behavior in the shallow portion of a subduction zone will help us prepare for future large tsunamis along the Japan-Kuril Trench.

Stress Release Process Along an Intraplate Fault Analogous to the Plate Boundary: A Case Study of the 2017 M5.2 Akita‐Daisen Earthquake, NE Japan

AbstractStress accumulation and release inside the plate remains poorly understood compared to that at the plate boundaries. Spatiotemporal variations in foreshock and aftershock activities can provide key constraints on time‐dependent stress and deformation processes inside the plate. The 2017 M5.2 Akita‐Daisen intraplate earthquake in NE Japan was preceded by intense foreshock activity and triggered a strong sequence of aftershocks. We examine the spatiotemporal distributions of foreshocks and aftershocks and determine the coseismic slip distribution of the mainshock. Our results indicate that seismicity both before and after the mainshock was concentrated on a planar structure with N‐S strike that dips steeply eastward. We observe a migration of foreshocks toward the mainshock rupture area, suggesting the possibility that foreshocks were triggered by aseismic phenomena preceding the mainshock rupture. The mainshock rupture propagated toward the north, showing less slip beneath foreshock regions. The stress drop of the mainshock was 1.4 MPa, and the radiation efficiency was 0.72. Aftershocks were intensely triggered near the edge of large coseismic slip regions where shear stress increased. The aftershock region expanded along the fault strike, which can be attributed to the postseismic aseismic slip of the mainshock. We find that the foreshocks, mainshock, aftershocks, and postseismic slip released stress at different segments along the fault, which may reflect differences in frictional properties. Obtained results were similar to those observed for interplate earthquakes, which supports the hypothesis that the deformation processes along plate boundaries and intraplate faults are fundamentally the same.

Comprehensive Detection of Very Low Frequency Earthquakes Off the Hokkaido and Tohoku Pacific Coasts, Northeastern Japan

AbstractVery low frequency earthquakes (VLFEs), classified as one type of slow earthquake, occur near seismogenic zones and can be a proxy for interplate slow slip. We investigated VLFE activity off the Hokkaido and Tohoku Pacific coasts, where the Pacific plate subducts under the North American plate. Comprehensive detection of VLFEs is performed for the period from January 2003 to July 2018 by a matched‐filter technique utilizing synthetic waveforms calculated based on a three‐dimensional velocity structure model. The spatiotemporal consistency between the afterslip of the 2003 Tokachi‐Oki earthquake (Mw 8.0) and VLFE distribution off the Hokkaido coast suggests that VLFE activity can reflect interplate slow slip. Inside a large coseismic slip area of the 2011 Tohoku earthquake (Mw 9.0), the VLFE activity was low thereafter, whereas outside the area, VLFE activity increased after the 2011 Tohoku earthquake. These characteristics are consistent with aseismic slip distributions estimated from repeating earthquakes. VLFEs were sometimes activated by afterslips of interplate earthquakes with Mw of 6–7, such as the 2008 Fukushima‐Oki earthquake and aftershocks of the 2011 Tohoku earthquake. Even in the coseismic slip areas of very large earthquakes, we found the occurrence of episodic bursts every 3 months to a year during an interseismic period between very large earthquakes. Such VLFE bursts may suggest small slips during the interseismic period.