Journal of Geophysical Research: Solid Earth最新文献

Volcanic eruptions are currently understood as triggered by increases in the overpressure of the magma storage regions, usually resulting in ground deformation. We assess whether observations of ground deformation can provide insights on the triggering mechanisms of sub-Plinian and Plinian eruptions, which are the most hazardous eruptions with a global impact. We process and compile InSAR and GNSS time series from 1991 to 2025 spanning four eruptions of this type in the Southern Andes: Hudson 1991, Chaitén 2008–2009, Cordón Caulle 2011–2012 and Calbuco 2015, resulting in the subduction zone with the largest erupted mass during 1980–2019. Only Cordón Caulle displays the theoretical pattern of pre-eruptive uplift due to reservoir pressurization, co-eruptive subsidence due to magma extraction, and post-eruptive uplift in response to magma inflow. For the rest of the volcanoes, we observe co- or post-eruptive ground deformation, but the data temporal resolution is low and did not sample well all the eruptions. On a global scale, InSAR and GNSS data recorded at volcanoes in subduction zones that experienced similar eruptions indicate few well-recorded eruptions. Only Okmok records a similar pattern to that of Cordon Caulle, while in other volcanoes geodetic data recorded the last episodes of pre-eruptive reservoir pressurization. This implies that most of the magma that increased the overpressure could have been emplaced in the decades or centuries prior to eruption and geodetic observations, or emplaced undetected. The longer time scales of recharge in subduction zone volcanoes compared with basaltic volcanoes in hot spots could indicate larger storage regions.

Seismicity during non-eruptive periods is useful for observing stress changes related to magmatic transport and volatile exsolution within active volcanoes. Mount St. Helens in Washington, USA, is the most active volcano in the continental United States and has been in quiescence since 2008. To explore the processes driving seismicity at Mount St. Helens, we create a high-resolution seismicity catalog of non-eruptive seismicity from 2008 through 2023, consisting of 31,133 events. We find persistent shallow seismicity (−2.2 to 2 km below sea level (BSL), 0–4.2 km below the surface) throughout the entire study period that concentrates beneath the dacite dome complex from the 1980–1986 and 2004–2008 eruptions. Additionally, there is frequent deeper seismicity (2–8 km BSL, 4.2–12.2 km below the surface) beginning in 2016. We examine a selection of deep earthquake swarms and find complex along-depth seismicity patterns. Within swarms, increases in shallow seismicity rates can precede or are concurrent with increases of deep seismicity rates. Lastly, we discover a series of semi-periodic, shallow, burst-like swarms, consisting of low-amplitude, repetitive similar earthquakes, indicating periodic valve-like release of fluid pressure from the conduit. Increased seismic activity beginning in 2016 indicates ongoing repressurization within the magmatic system driven by recharge or crystallization-induced second boiling within the upper-crustal reservoir after 2008. The data indicate that non-eruptive seismicity at Mount St. Helens is controlled by fluid pressure changes from gas flux sourced from the magma reservoir that migrates through crack networks.

Using dense seismic data sets, we present a new 3D velocity model of Taiwan that images a prominent mid-crustal (∼20–30 km) high-velocity body beneath west-central Taiwan. The inclusion of high-quality post-2012 recordings from the Central Weather Administration Seismic Network (CWASN) ensures the elimination of uncorrectable timing errors. In addition, a machine learning–based phase picker was applied to the entire data set to improve the consistency and accuracy of phase arrival identification. The resulting model generally aligns with previous tomographic studies. Structures inferred from velocity gradients in the tomographic profiles largely correspond to mapped faults and geological unit boundaries in Taiwan. The model also images a pronounced mid-crustal (∼20–30 km) high-velocity anomaly beneath west-central Taiwan. Under representative P–T conditions, Vp–Vs–density comparisons indicate the best match with mafic compositions, though the interpretation is not unique. This mafic interpretation is compatible with passive-margin mafic additions (underplating and/or intrusions). The anomaly coincides with reduced seismicity below ∼20 km and depth-dependent stress orientations, consistent with a relatively competent mid-crustal volume. Geological and geophysical similarities with the Dongsha Rise further suggest a possible shared tectonic and magmatic origin, likely linked to mafic underplating during South China Sea rifting. These findings improve our understanding of structural highs along passive continental margins and their role in influencing crustal deformation in the Taiwan orogen. The new model also provides a robust framework for future waveform-based seismic imaging.

The shared tectonic history of southwestern Australia and East Antarctica facilitates the exchange of geological insights between the regions. In this study, we present coupled susceptibility and density models obtained through the joint inversion of magnetic and gravity data. By assuming a common geological source for both signals, our coupling method minimizes misfits and variation in information, thereby enhancing a correlation between susceptibility and density. The resulting anomalies demonstrate structural continuity between the continents, aligning closely with major shear zones and seismic reflectors. Combining these results with machine learning, geochemical, and petrophysical databases, we predict a high-resolution (10 km) heat production map for East Antarctica. Utilizing a Markov Chain Monte Carlo (MCMC) algorithm, we further develop a geothermal heat flow map with greater spatial variability than previous studies, yielding an average of $��55�$mW/$��m^2�$ in East Antarctica and $��46�$mW/$��m^2�$ in southwestern Australia. Our results provide a crucial high-resolution boundary condition for ice sheet simulations, enabling more realistic estimates of basal meltwater production and ice temperatures.

An earthquake record is the convolution of source radiation, path propagation and site effects, and instrument response. Isolating the source component requires solving an ill-posed inverse problem. Whether the instability of inferred source parameters arises from varying properties of the source, or from approximations we introduce in solving the problem, remains an open question. Such approximations often derive from limited knowledge of the forward problem. The Empirical Green's function (EGF) approach offers a partial remedy, by approximating the forward response of large events using the records of smaller events. The choice of the best small event drastically influences the properties estimated for the larger earthquake. Discriminating variability in source properties from epistemic uncertainties, stemming from the forward problem or other modeling assumptions, requires us to reliably account for, and propagate, any bias or trade-off introduced in the problem. We propose a Bayesian inversion framework that aims at providing reliable and probabilistic estimates of source parameters (here, for the source-time function or STF), and their posterior uncertainty, in the time domain. We jointly solve for the best EGF using one or a few small events as prior EGF. Our approach expands on DeepGEM, an unsupervised generalized expectation-maximization framework for tomography. We demonstrate, with toy models and various applications to mainshocks of $��M_W�$ ranging from $��\sim �$4 to 6.3, the potential of DeepGEM-EGF to disentangle the variability of the seismic source from biases introduced by modeling assumptions.

We investigate seismic wave amplification in Nenana basin, central Alaska, using 3D seismic wavefield simulations. We quantify frequency-dependent amplification by comparing synthetic seismograms among four different seismic velocity models: (a) a tomographic model, (b) a tomographic model with the uppermost 6.5 km replaced by a 1D basin profile, (c) a tomographic model with an embedded ellipsoidal basin, and (d) a tomographic model with an embedded realistic basin. For each model we perform wavefield simulations accurate up to 2 Hz for a set of 10 different earthquakes, which provide a range of frequencies and incident angles for waves interacting with the basin. Average amplification ratios are four on the horizontal components and seven on the vertical component. The dominant influence of the amplification is the 3D geometry of the basin, not the slow-velocity profile near the surface. Our synthetic amplification ratios are in general agreement with amplification estimates obtained from 14 stations that recorded the same set of earthquakes. Our approach offers a general strategy for documenting frequency-dependent basin amplification for a region with realistic basin structures and local earthquakes.

Cenozoic volcanic rocks in East Asia are widespread across subduction zones, oceanic plates, and continental interiors. The generation of these volcanic materials is closely associated with partial melting of the upper mantle and the stagnation of the Pacific slab in the mantle transition zone. However, the spatial distribution and migration of melts in the upper mantle remain poorly understood. Here we develop an updated tomographic approach for P-wave tilting-axis anisotropy and apply it to the East Asian region. Our model reveals significant anisotropy in the upper mantle beneath volcanic fields, as well as in the lower mantle underlying the stagnant slab. The anisotropy in the subduction zone is too strong to be caused by only lattice-preferred orientation of peridotite; instead, it can be partly attributed to shape-preferred orientation of elongated/flat pores within melt-rich bands. By examining the hypothesis that the primary mechanism of anisotropy is the alignment of pores filled by melt, we identify a pervasive melt layer at ∼300 km depth beneath East China, with segments rising toward the base of the lithosphere beneath intraplate volcanic centers. Through quantifying the spatial distribution of melt, including its volume fraction and pore aspect ratio, our tomography illustrates the organization and migration of melt in relation to intraplate volcanism. This study emphasizes the significance of the melt pores' shape-preferred orientation in understanding anisotropy in the upper mantle and uppermost lower mantle.

Observations of fluid-driven swarm seismicity expanding with the same diffusive space-time behavior as analytical solutions for aseismic slip have been interpreted as evidence that stress changes from aseismic slip trigger seismic slip. In some cases, aseismic slip is confirmed from crustal deformation measurements or sheared wellbore casing. Our work offers another interpretation of migrating seismicity that may be relevant when there is no independent evidence for aseismic slip. We present 2D earthquake sequence models that simulate constant-pressure fluid injection into a velocity-weakening rate-and-state fault, permeability enhancement with slip, and fluid transport. We also derive an analytical expression for a unilateral fluid-driven aseismic shear crack with constant friction and permeability enhancement. Our numerical results show that pressure diffusion and elastic stress transfer from seismic slip drive seismicity fronts that expand diffusively outward from the injector, and that analytical solutions for aseismic slip match this seismicity pattern, even when almost all slip is seismic. Aseismic slip at the slip front increases permeability, allowing fluid influx and pressurization, weakening the fault prior to slipping seismically. Adding roughness to the fault introduces heterogeneous fault normal stress, resulting in a broader distribution of event sizes, distributed seismicity behind the slip front, and swarm-like clusters of microseismicity. Even with this complexity, the nonplanar simulations produce a diffusively expanding slip front and mostly seismic slip. Our results suggest that aseismic slip solutions can be used to quantitatively interpret the space-time behavior of migrating swarms, even in cases with negligible measured aseismic slip.