Deep Tremor Research Articles

Duplex Underplating, Sediment Dehydration and Quartz Vein Mineralization in the Deep Tremor Source Region

AbstractDeep tectonic tremor downdip of the seismogenic zone in warm subduction zones is thought to occur in the region of high fluid pressures. However, the deformation and fluid processes responsible for tremor are poorly understood. We examined the Tomuru metamorphic rocks on Ishigaki Island, southern Ryukyu Arc, deformed at ∼40 km depth and ∼450°C under epidote‐blueschist metamorphism comparable to the tremor source region in northern Cascadia subduction zone. Here, quartz vein‐rich metapelite and metabasite are repeated many times as a result of duplex underplating. The spatiotemporal relationship between clustered quartz veins and the juxtaposition of metapelite and metabasite suggests that quartz vein formation and duplex underplating are contemporaneous. Viscous shear in metapelite is accommodated by dissolution‐precipitation creep. Metabasite records heterogeneous dehydration, resulting in rheological heterogeneity characterized by greenschist lenses in the foliated blueschist matrix. Viscous shear in the blueschist matrix was mainly accommodated by dissolution‐precipitation creep of glaucophane. Geochemical and strontium‐neodymium isotope analyses indicated that quartz veins were derived from sediment dehydration, whereas dehydration from oceanic crust contributed neither to quartz vein formation nor to fluid overpressures. We suggest that high fluid pressure in the deep tremor source region is primarily controlled by dehydration of subducting sediments, and the clustered quartz veins in underplated rocks correlate with the overpressured tremor source in low shear‐wave velocity zones.

Deep Short‐Term Slow Slip and Tremor in the Manawatu Region, New Zealand

AbstractThe Manawatu region experiences deep tremor and long‐term slow slip events (SSEs); however, tremor is adjacent to, and not co‐located with, long‐term SSEs. Observations of episodic tremor and slip (ETS) elsewhere suggest it is possible smaller short‐term SSEs below the current detection threshold occur where tremor is observed. Therefore, we sought to determine if small SSEs occurred with Manawatu tremor. We decomposed GNSS data using times of tremor to assess average surface displacements and performed a static slip inversion to model the displacement during tremor. The slip inversion suggested small slow slip partially coincided with tremor and long‐term SSEs may influence these small SSEs by increasing slip rates. We suggest that the interface below deep long‐term SSEs may slip often, in small ETS‐like SSEs that are not individually detectable geodetically. The question remains as to the nature of the strong variability in SSE behavior with depth and duration in the southern Hikurangi margin.

Complex Interaction, Striations, and Periodicity of Deep Tremor Surrounding a Tremor Gap in the Central Nankai Subduction Zone, Japan

AbstractThe Nankai subduction zone is characterized by a belt of deep tremor extending from western Shikoku to the Tokai region and a tremor seismicity gap beneath the Kii Channel between Shikoku and the Kii Peninsula. Tremor activities near the gap are not well understood because of poor seismic network coverage. In this study, we conducted an observation campaign in eastern Shikoku to investigate the detailed tremor activity across the tremor gap. The new tremor catalog shows high detectability and resolution, with tremor clusters in both eastern Shikoku and the western Kii Peninsula having distinct shapes. We discovered characteristic time intervals between tremor activity on both sides of the gap, suggesting the occurrence of undetected slow slip events (SSEs) within the gap that propagated approximately 10 km/day. We also found a relationship between the tremor activities and a shallower long‐term SSE. Our examination of the detailed distribution of tremor events showed a distinct striation pattern that may be associated with the history of the subducting plate motion and the plate geometry, and our examination of their periodicity showed spatial variations in the dominant period of tremor activity that likely reflect the heterogeneous physical properties of the plate interface.

Frictional stability and hydromechanical coupling of serpentinite-bearing fault gouge

SUMMARY Observations of slow earthquakes and tremor have raised fundamental questions about the physics of quasi-dynamic rupture and the underlying fault zone processes. The presence of serpentinite at P-T conditions characteristic of deep tremor and slow earthquakes suggests that it plays an important role in controlling complex fault slip behaviour. Here, we report on experiments designed to investigate the frictional behaviour of serpentinite sampled from outcrop exposures (SO1 and SO2) of altered ultramafic rocks present at depth, and recovered from the SAFOD borehole (G27). XRD analyses reveal the presence of chrisotyle, lizardite, kaolinite, talc in SO1; lizardite, clinochlore and magnetite in SO2; and lizardite, quartz and calcite in G27. We sheared fault gouge in a double-direct shear configuration using a true triaxial deformation apparatus. The effective normal stress was varied from 2 to 40 MPa. We conducted velocity stepping tests and slide-hold-slide (SHS) tests in each experiment to characterize frictional stability and healing. At the end of each experiment, post-shear permeability was measured and the samples were recovered for microstructural analysis. The steady-state friction coefficient was μ = 0.17 for SO1, μ = 0.33 for SO2 and μ = 0.53 for G27. Overall, the gouges exhibit velocity strengthening behaviour, and become nearly velocity neutral at 40 MPa effective normal stress. SHS tests show positive healing rates for SO2 and G27, whereas SO1 exhibits zero or negative healing rates. Permeability decreases with increasing σn’, with SO1 (k = 10–20 m2) showing the lowest values. Microstructural observations reveal a well-developed R-Y-P fabric in SO1, which is not observed in SO2 and G27. We posit that the development of shear fabric controlled by mineralogy governs frictional and hydrological properties. In this context, when serpentinite is associated with other weak phyllosilicate minerals, frictional stability and hydrological properties can vary greatly, with a potential control on the mode of fault failure.

A likely geological record of deep tremor and slow slip events from a subducted continental broken formation

Fluids in subduction zones play a key role in controlling seismic activity, drastically affecting the rheology of rocks, triggering mineral reactions, and lowering the effective stress. Fluctuating pore pressure is one important parameter for the switch between brittle and ductile deformation, thus impacting seismogenesis. Episodic tremor and slow slip events (ETS) have been proposed as a common feature of the geophysical signature of subduction zones. Their geological record, however, remains scanty. Only the detailed and further characterization of exhumed fossil geological settings can help fill this knowledge gap. Here we propose that fluctuating pore pressure linked to metamorphic dehydration reactions steered cyclic and ETS-related brittle and ductile deformation of continental crustal rocks in the subduction channel of the Apennines. Dilational shear veins and ductile mylonitic shear zones formed broadly coevally at minimum 1 GPa and 350 °C, corresponding to ~ 30–40 km depth in the subduction zone. We identify carpholite in Ca-poor metasediments as an important carrier of H2O to depths > 40 km in cold subduction zones. Our results suggest that the described (micro)structures and mineralogical changes can be ascribed to deep ETS and provide a useful reference for the interpretation of similar tectonic settings worldwide.

Dynamic triggering of earthquakes in the North Island of New Zealand following the 2016 Mw 7.8 Kaikōura earthquake

Large earthquakes are capable of triggering microseismicity, deep tremor and slow-slip events from intermediate- to long-distance ranges. Unfortunately, earthquake catalogs are typically incomplete right after large mainshocks. Hence, mapping triggering patterns and understanding the underlying triggering mechanism are challenging. Here we present two different types of seismicity responses to dynamic stressing by passing seismic waves in the North Island of New Zealand following the 2016 Mw 7.8 Kaikōura earthquake. Based on a template matching technique, we identify up to 4-7 times more earthquakes than listed in New Zealand's GeoNet catalog. We also compute the dynamic stress perturbations in the North Island due to the Kaikōura mainshock and compare them to seismicity rate changes to identify regions with high susceptibility to dynamic stress triggering. Abundant triggered earthquakes occurred immediately following the mainshock in the shallow crust around the active Taupo Volcano Zone, likely related to activation of crustal faults/fluids associated with back-arc rifting and volcanism. Approximately 8 days after the initial dynamic stressing, an active burst of seismicity with the largest event of ML 5.55 occurred along the shallow megathrust near Porangahau on the east coast of the North Island. This burst of seismicity is likely driven by a ∼Mw 7.1 shallow slow slip event dynamically triggered by the mainshock. Our findings reveal the heterogeneous nature of dynamic triggering in a plate boundary region with recent large earthquake sequences and aseismic transient events and further highlight the difficulties in time-dependent earthquake forecasting following large mainshocks.

High resolution location of deep low-frequency tremors beneath the Kii Peninsula, Nankai subduction zone, Japan, using data from a dense seismic array

SUMMARY This study performs detection and location of deep low-frequency tremors beneath the Kii Peninsula, Nankai subduction zone, Japan, using data from a dense seismic array. We set a quantitative threshold for the tremor detection based on the Gaussian distribution of waveform coherence among stations to distinguish between tremor signal and noise. Then, we estimated slownesses and arrival azimuths by applying the Multiple Signal Classification method and performed hypocentre determination by backprojection onto the plate interface. During the analysed period of 2 yrs from July 2012 to July 2014, we detected 25155 tremor events which are approximately 2.2 times more than those in the AIST-tremor catalogue based on the conventional envelope correlation method ( 11475 events). This improvement is due to the detection of even weak amplitude tremors owing to the array analysis scheme, which uses recorded waveform’s phase information. Our high-resolution tremor catalogue leads to the following findings of the tremor activity in the Kii Peninsula. A few tremor episodes show continuous updip migration in the initial stage. The updip migration speed depends on whether the tremor migrates in the along-strike direction after the updip migration: approximately 1.0 km hr –1 for tremors that develop into the along-strike migration, and approximately 0.5 km hr–1 for those that do not. Estimated radiated energies are found to increase gradually with propagation into the updip direction. These findings suggest the depth dependence of the frictional strength on the plate interface. Furthermore, we noticed that accumulated radiated energies are positively correlated with the updip migration speed, and this relationship implies that fluid migration might play a role in the updip migration.

Seismic energy radiation and along-strike heterogeneities of shallow tectonic tremors at the Nankai Trough and Japan Trench

Shallow slow earthquakes have been documented along shallow plate interfaces near trenches. Recent geophysical observation networks located offshore of Japan enable us to analyze shallow tremors in the Nankai Trough and the Japan Trench. Onshore seismic stations are also important for detecting shallow very low frequency earthquakes (VLFEs) and for evaluating their seismicity prior to the deployment of offshore observation networks. This study analyzes data from ocean bottom seismometers to estimate the seismic energy radiation of such tremors, from which we observe along-strike heterogeneity. Tremors with higher seismic energy rates tend to have longer recurrence intervals, which has also been observed for deep tremors. This study also estimates seismic moment releases of shallow VLFEs at the Japan Trench observed by onshore seismic stations using Green's function in a local three-dimensional seismic velocity model. The scaled energy, which is the ratio of the seismic energy (rate) to the seismic moment (rate), is ~10−9. Shallow slow earthquakes located off the Kii Peninsula and Cape Muroto in the Nankai Trough have higher values (10−9–10−8), while shallow slow earthquakes located off the Kii channel in the Nankai Trough and in the Japan Trench have lower values (10−10–10−9), which are similar to the values estimated for deep slow earthquakes. By comparing the cumulative seismic energy of the shallow tremors with the cumulative seismic moment of shallow VLFEs, we evaluate the monitoring of shallow tremors and shallow VLFEs in the Japan Trench, suggesting that monitoring shallow VLFEs based on data from onshore seismic stations could miss many (~90% at most) of the seismic moment releases by small magnitude but frequent events.

Does Deep Tectonic Tremor Occur in the Central‐Eastern Mediterranean Basin?

AbstractTectonic tremor has been observed at the roots of many fault systems around the Pacific rim, including convergent and transform plate boundaries. The extent to which deep tremor signals are prevalent along fault systems elsewhere, including the Mediterranean basin, has not yet been documented in detail. A body of evidence suggests that tremor triggered during the surface waves of teleseismic events may commonly occur where ambient tremor during episodic tremor and slip episodes occur, suggesting triggered tremor provides a useful tool to identify regions with ambient tremor. We perform a systematic search of triggered tremor associated with large teleseismic events between 2010 and 2020 at four major fault systems within the central‐eastern Mediterranean basin, namely the Hellenic and Calabrian subduction zones, and the North Anatolian and Kefalonia transform faults. In addition, we search for ambient tremor during a slow slip event in the eastern Sea of Marmara along a secondary branch of the North Anatolian Fault, and two slow slip events beneath western Peloponnese (Hellenic Subduction Zone). We find no unambiguous evidence for deep triggered tremor, nor ambient tremor. The absence of triggered tremor at the Hellenic and Calabrian subduction zones supports an interpretation of less favorable conditions for tremorgenesis in the presence of old and cold slabs. The absence of tremor along the transform faults may be due to an absence of the conditions commonly promoting tremorgenesis in such settings, including high‐fluid pressures and low‐differential stresses between the down‐dip limit of the seismogenic layer and the continental Moho.

Estimation of fault models for short-term slow\xa0slip events from groundwater pressure in soft sedimentary layers

Deep low-frequency tremors and short-term slow slip events (SSEs) are known to occur along the Nankai Trough in Japan. Although short-term SSEs are thought to occur repeatedly in the northern part of Ise Bay, deep low-frequency tremors are not observed there. Because the area around the northern part of Ise Bay is characterized by soft sedimentary layers not suitable for strainmeter or tiltmeter installation, there are no high-quality crustal deformation observation sites in the area. Accordingly, the local extent of slip of short-term SSEs has not been confirmed. We significantly improved the crustal strain sensitivity of the groundwater level (pressure) in the inner pipe of the observation well at the Hokusei observation site (HKSi, northwest of Ise Bay) by sealing it with a packer. Consequently, we were able to observe groundwater pressure changes related to slow slip at the plate boundary. We estimate that slip of short-term SSEs during July 2016, November 2017, and April 2018 extended to the northern part of Ise Bay. Furthermore, groundwater pressure fluctuations at HKSi in April 2018 greatly improved the SSE fault model, confirming that slow slip occurs in the area, despite the absence of deep low-frequency tremor. The slips without tremors are a characteristic of the northern area of Ise Bay, differing from other areas of the Nankai Trough. Our results demonstrate that groundwater level/pressure fluctuations are a powerful tool for crustal deformation observations in areas characterized by soft sedimentary layers.

Fluid overpressure from chemical reactions in serpentinite within the source region of deep episodic tremor

Slow fault slip includes a range of transient phenomena that occur over timescales longer than those of standard earthquakes. Slow slip events are often closely associated with swarms of tectonic tremor. Deep episodic tremor and slip close to the slab–mantle interface in subduction zones has been linked to high fluid pressures produced by dehydration of the subducting slab at greater depths. The slab–mantle interface is a fundamental chemical boundary, where mantle rocks are sheared and mixed with oceanic slab lithologies in a highly reactive environment to form serpentinite. Here we present field and microstructural observations from the plate boundary-scale crustal Livingstone Fault in New Zealand that suggest chemical reactions involving serpentinite can promote rock hardening and generate in situ fluid overpressures. We infer that these processes collectively can result in hydrofracturing and a transition from distributed creep to localized brittle failure and faulting. Serpentinite-related reactions occur over a wide range of pressure and temperature conditions that overlap with those in many forearc mantle wedges. We conclude that the release of fluids derived from such reactions may be an additional and widespread mechanism to generate high fluid pressure patches and brittle failure in the source region of deep tremor along the slab–mantle interface. Chemical reactions between slab and mantle rocks may lead to brittle failure where deep episodic tremor occurs in subduction zones, according to field and microstructural observations of a shear zone in New Zealand.

Development of a modified envelope correlation method based on maximum-likelihood method and application to detecting and locating deep tectonic tremors in western Japan

We develop a modified envelope correlation method for locating deep tectonic tremors and apply it to construct a tremor catalog for western Japan. We redefine the envelope cross-correlation method as a maximum-likelihood method by using the cross-correlation functions as objective functions and then weighting components of the data by the inverse of the error variances. This method is also capable of detecting multiple sources that occur almost simultaneously because they appear as local maxima in our analysis. We employ a nonlinear function, the average of the weighted cross-correlation functions (ACC), to locate the deep tectonic tremor hypocenters. Our optimization method is performed in two steps. We first fix the source depth and use a grid search to find the local ACC maxima, which are the potential event locations. We then use each potential event location as an initial value and apply the gradient method to determine its hypocentral location. Several source locations are sometimes determined in a 5-min time window. We also perform a numerical test using synthetic waveforms to validate our tremor hypocenter estimations. We apply our proposed method to continuous seismograms in western Japan for 12.5-year period, with our new approach detecting 35% more tremors than the envelope correlation method with the outlier control owing to the detection of multiple tremors in a single time window and to the improved tremor hypocenter accuracy yielded by the appropriate weighting scheme. We estimate the spatial resolution, which is defined as the epicentral distance between sources that can be distinguished by the location method, to be ~ 100 km.

Dehydration-induced rheological heterogeneity and the deep tremor source in warm subduction zones

Dehydration-induced rheological heterogeneity and the deep tremor source in warm subduction zones

Resolving the Detailed Spatiotemporal Slip Evolution of Deep Tremor in Western Japan

AbstractWe study the detailed spatiotemporal behavior of deep tremor in western Japan through the development and application of a new slip inversion method. Although many studies now recognize tremor as shear slip along the plate interface manifested in low‐frequency earthquake (LFE) swarms, a conventional slip inversion analysis is not available for tremor due to insufficient knowledge of source locations and Green's functions. Here we introduce synthetic template waveforms, which are typical tremor waveforms obtained by stacking LFE seismograms at arranged points along the plate interface. Using these synthetic template waveforms as substitutes for Green's functions, we invert the continuous tremor waveforms using an iterative deconvolution approach with Bayesian constraints. We apply this method to two tremor burst episodes in western and central Shikoku, Japan. The estimated slip distribution from a 12 day tremor burst episode in western Shikoku is heterogeneous, with several patchy areas of slip along the plate interface where rapid moment releases with durations of <100 s regularly occur. We attribute these heterogeneous spatiotemporal slip patterns to heterogeneous material properties along the plate interface. For central Shikoku, where we focus on a tremor burst episode that occurred coincidentally with a very low frequency earthquake (VLF), we observe that the source size of the VLF is much larger than that estimated from tremor activity in western Shikoku. These differences in the size of the slip region may dictate the visibility of VLF signals in observed seismograms, which has implications for the mechanics of slow earthquakes and subduction zone processes.

Tidal Response in Shallow Tectonic Tremors

AbstractVarious types of slow earthquakes (e.g., tectonic tremors and slow slip events) have been reported in tectonic zones, especially in the subduction zone. The tidal response of a tremor is considered to be strongly related to the weak friction state of the plate interface, and many studies have reported observational evidence of such correlation between tides and deep tremor activity. Here we used the modified frequency scanning method at a single station to detect micro tectonic tremors that have not been previously reported in southern Kyushu. In the early stage of the tremor activity, tremors are mostly modulated by slow slip events. In contrast, we found a seismic response to ocean tides during the later stage in the shallower part of the subduction zone. This might indicate that the tremors are triggered by tidal changes caused by fault weakening due to slow slip events as same as deeper condition.

Imaging the nonvolcanic tremor zone beneath the San Andreas fault at Cholame, California using station-pair double-difference tomography

Nonvolcanic tremors have been detected deep beneath the San Andreas fault (SAF) near Cholame, California. The tremors are modulated by small stress changes induced by Earth tides and regional and teleseismic earthquakes, implying elevated pore fluid pressure in the tremor zone. In this area, tremors lie beneath the seismogenic zone, limiting the usefulness of local earthquakes for resolving seismic velocity properties in the tremor zone. Station-pair double-difference tomography that uses differential tremor arrival times is used, for the first time, to provide new detailed information about the complexity of the lower-crust and upper-mantle transition and the occurrence of deep tremors in zones of localized low shear wave velocity anomalies. The anomalies may represent zones containing high-pore pressure fluids that migrate into the tremor zone episodically from the southwest and that are ultimately derived from dehydration of deep serpentinized mantle wedge material. These results improve our understanding of the tremor process, why tremors are concentrated in specific zones along the SAF, and possible relationships between tremors and large historic earthquakes.

Spatiotemporal evolution of slow slip events in a nonplanar fault model for northern Cascadia subduction zone

AbstractSlow slip events (SSEs) are identified as the quasi‐stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones. In the well‐instrumented Cascadia margin, a class of Mw6.0 slow slip events arise beneath Port Angeles every ∼14 months, as inferred from two decades of continuous geodetic monitoring. The along‐strike bending of the incoming oceanic plate beneath north Washington is a unique geometric feature whose influence on slow slip processes is still unknown. Here we incorporate a realistic fault geometry of northern Cascadia in the framework of rate‐ and state‐dependent friction law, to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault. The modeled SSEs capture the major characteristics revealed by GPS observations. The central 150 km long fault segment beneath Port Angeles acts as a repetitive slip patch, where SSEs appear every ∼1.5 years with a maximum slip of ∼2.5 cm. Two minor slip patches with smaller areas and cumulative slips straddle this central slip patch. The along‐strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone, suggesting strong geometrical control on the slow slip process. This correlation holds even after removing the effect of W/h∗, ratio between velocity‐weakening SSE fault width and characteristic nucleation size. Besides the GPS‐detectable fast‐spreading phase, we find that each SSE cycle consists of deep pre‐SSE preparation and post‐SSE relaxation phases, which may be the driving mechanism for the deep tremor activity between major SSE episodes discovered in Cascadia.

Origin of the Arima-type and Associated Spring Waters in the Kinki District, Southwest Japan

Rare earth elements (REEs) of the spring waters upwelling in the non-volcanic fore-arc region of the Kinki district in southwest Japan were investigated to assess their upwelling processes and deep-seated origins. A principal component analysis of the REE data identified three principal components (PCs) that cover 89% of the entire sample variance: (1) PC-01, which corresponds to a dilution process by which fluids are introduced at low concentrations, previously represented by major solute binary trends, including δ18O–δD systematics; (2) PC-02, which is a precipitation process of REEs from the brine; and (3) PC-03, which is an incorporation of REEs from country rock by carbonic acidity, although the types of country rocks may also have a significant impact on the spring water compositions. Based on these three PCs, together with the major solute concentrations and hydrogen, oxygen, and helium isotopic compositions determined in previous studies, five distinct types of spring waters in the Arima and Kii areas were identified: (i) “Tansansen”, (ii) “Kinsen”, (iii) “Ordinary Arima”, (iv) “Ginsen”, and (v) “Eastern Kii”. These five types probably represent (ii) a deep brine, (iii) an evolved deep brine that precipitated REE-bearing minerals, (iv) a mixture of (iii) and meteoric water, (v) a meteoric water carbonated by deep gas derived from (ii), and (i) a spring water similar to (v) with a more significant influence of the country rock constituting the aquifer. A comparison of the spring waters in the Arima and Kii areas revealed systematic geographic distributions. The “Ordinary Arima”-type occurs along the Median Tectonic Line, and the “Eastern Kii”-type occurs in the eastern part of the Kii area. The latter seems to upwell in the restricted region where deep low-frequency tremors are observed. We suggest that the geographical distributions are linked to the tectonic setting and/or temporal evolution of fluid upwelling.

Delayed dynamic triggering of deep tremor along the Parkfield‐Cholame section of the San Andreas Fault following the 2014 M6.0 South Napa earthquake

AbstractLarge, distant earthquakes are known to trigger deep tectonic tremor along the San Andreas Fault and in subduction zones. However, there are relatively few observations of triggering from regional distance earthquakes. Here we show that a small tremor episode about 12–18 km NW of Parkfield was triggered during and immediately following the passage of surface waves from the 2014 Mw 6.0 South Napa main shock. More notably, a major tremor episode followed, beginning about 12 h later, and centered SE of Parkfield near Cholame. This major episode is one of the largest seen over the past several years, containing intense activity for ~3 days and taking more than 3 weeks to return to background levels. This episode showed systematic along‐strike migration at ~5 km/d, suggesting that it was driven by a slow‐slip event. Our results suggest that moderate‐size earthquakes are capable of triggering major tremor and deep slow slip at regional distances.

Linking magma transport structures at Kīlauea volcano

AbstractIdentifying magma pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long‐period (LP) events dominate the shallow (5–10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending magma. Using envelope cross‐correlation, we systematically catalog non‐earthquake seismicity between 2008 and 2014. We find that the LPs and deep tremor are spatially distinct, separated by the 15–25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader band (0.5–20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the MFZ. We propose that the overlying MFZ promotes lateral magma transport, linking this deep intrusion with Kīlauea's shallow magma plumbing.