Following the 15 January 2022 Hunga Tonga‐Hunga Ha'apai eruption, several trace gases measured by the Aura Microwave Limb Sounder (MLS) displayed anomalous stratospheric values. Trajectories and ...radiance simulations confirm that the H2O, SO2, and HCl enhancements were injected by the eruption. In comparison with those from previous eruptions, the SO2 and HCl mass injections were unexceptional, although they reached higher altitudes. In contrast, the H2O injection was unprecedented in both magnitude (far exceeding any previous values in the 17‐year MLS record) and altitude (penetrating into the mesosphere). We estimate the mass of H2O injected into the stratosphere to be 146 ± 5 Tg, or ∼10% of the stratospheric burden. It may take several years for the H2O plume to dissipate. This eruption could impact climate not through surface cooling due to sulfate aerosols, but rather through surface warming due to the radiative forcing from the excess stratospheric H2O.
Plain Language Summary
The violent Hunga Tonga‐Hunga Ha'apai eruption on 15 January 2022 not only injected ash into the stratosphere but also large amounts of water vapor, breaking all records for direct injection of water vapor, by a volcano or otherwise, in the satellite era. This is not surprising since the Hunga Tonga‐Hunga Ha'apai caldera was formerly situated 150 m below sea level. The massive blast injected water vapor up to altitudes as high as 53 km. Using measurements from the Microwave Limb Sounder on NASA's Aura satellite, we estimate that the excess water vapor is equivalent to around 10% of the amount of water vapor typically residing in the stratosphere. Unlike previous strong eruptions, this event may not cool the surface, but rather it could potentially warm the surface due to the excess water vapor.
Key Points
Following the Hunga Tonga‐Hunga Ha'apai eruption, the Aura Microwave Limb Sounder measured enhancements of stratospheric H2O, SO2, and HCl
The mass of SO2 and HCl injected is comparable to that from prior eruptions, whereas the magnitude of the H2O injection is unprecedented
Excess stratospheric H2O will persist for years, could affect stratospheric chemistry and dynamics, and may lead to surface warming
Determining earthquake hypocenters and focal mechanisms requires precisely measured P wave arrival times and first‐motion polarities. Automated algorithms for estimating these quantities have been ...less accurate than estimates by human experts, which are problematic for processing large data volumes. Here we train convolutional neural networks to measure both quantities, which learn directly from seismograms without the need for feature extraction. The networks are trained on 18.2 million manually picked seismograms for the Southern California region. Through cross validation on 1.2 million independent seismograms, the differences between the automated and manual picks have a standard deviation of 0.023 s. The polarities determined by the classifier have a precision of 95% when compared with analyst‐determined polarities. We show that the classifier picks more polarities overall than the analysts, without sacrificing quality, resulting in almost double the number of focal mechanisms. The remarkable precision of the trained networks indicates that they can perform as well, or better, than expert seismologists.
Key Points
We train and validate convolutional neural networks to pick P wave arrival times and first‐motion polarities on 19.4 million seismograms
Arrival time picks are within 0.028 s of the analyst pick 75% of the time, and first‐motions are classified with 95% precision
The remarkable performance of the trained networks suggests that they can perform as well, or better, than human experts
SUMMARY
The Earth’s ellipticity of figure has an effect on the traveltimes of seismic waves over teleseismic distances. Tables of ellipticity corrections and coefficients have been used by ...seismologists for several decades; however, due to the increasing variety and complexity of seismic phases in use, current tables of ellipticity coefficients are now outmoded and incomplete. We present a Python package, EllipticiPy, for the calculation of ellipticity corrections, which removes the dependence on pre-calculated coefficients at discrete source depths and epicentral distances. EllipticiPy also facilitates the calculation of ellipticity corrections on other planetary bodies. When applied to both Earth and Mars, the magnitudes of ellipticity corrections are of the order of single seconds and are significant for some seismic studies on Earth but remain negligible on Mars due to other greater sources of uncertainty.
SUMMARY
An unbiased estimation of the b-value and of its variability is essential to verify empirically its physical contribution to the earthquake generation process, and the capability to improve ...earthquake forecasting and seismic hazard. Notwithstanding the vast literature on the b-value estimation, we note that some potential sources of bias that may lead to non-physical b-value variations are too often ignored in seismological common practice. The aim of this paper is to discuss some of them in detail, when the b-value is estimated through the popular Aki’s formula. Specifically, we describe how a finite data set can lead to biased evaluations of the b-value and its uncertainty, which are caused by the correlation between the b-value and the maximum magnitude of the data set; we quantify analytically the bias on the b-value caused by the magnitude binning; we show how departures from the exponential distribution of the magnitude, caused by a truncated Gutenberg–Richter law and by catalogue incompleteness, can affect the b-value estimation and the search for statistically significant variations; we derive explicitly the statistical distribution of the magnitude affected by random symmetrical error, showing that the magnitude error does not induce any further significant bias, at least for reasonable amplitude of the measurement error. Finally, we provide some recipes to minimize the impact of these potential sources of bias.
The large scale extraction of geothermal energy can reduce COsub.2 emissions. For hot dry rocks, the key to successful utilization depends on the efficiency of reservoir reconstruction. The chemical ...and thermal stimulation methods are always used in geothermal reservoir reconstruction except in hydraulic fracturing with high fluid injection pressure, which is believed to reduce the seismic hazard by applying before the high-pressure hydraulic fracturing stimulation. However, at the laboratory scale, there are still very limited experimental studies illustrating the combined effects of chemical and thermal stimulation on the permeability and mechanical properties of granite, which is regarded as the main type of hot dry rock. In this paper, comparative stimulation experiments were carried out, including thermal/cold stimulation, COsub.2 bearing solution hydro-chemical stimulation, combined thermal and COsub.2 bearing fluid stimulation. By means of nuclear magnetic resonance analysis, permeability test and triaxial compression test, the changes of the micro-structure, permeability and mechanical properties of granite under various stimulation conditions were analyzed. The experimental results show that, compared with the single thermal stimulation and COsub.2 bearing fluid hydro-chemical stimulation, the superposition effect of thermal and COsub.2 bearing fluid hydro-chemical stimulation can increase the number of micro-fractures in granite more effectively, thus increasing the permeability, while the elastic modulus and compressive strength decrease. Moreover, the cooling mode on the granite also has a certain influence on the stimulation effect. After water-cooling on the heated granite (300 °C), combined with the COsub.2 bearing fluid stimulation (240 °C, 20 MPa), the permeability of granite is the highest, increasing by 17 times that of the initial state, and the porosity also increases by 144.4%, while the elastic modulus and compressive strength decrease by 14.3% and 18.4%, respectively. This implies that the deterioration of mechanical properties due to the micro-fractures increased by the thermal and chemical stimulation can enhance the fluid conductivity and heat extraction of granite. The methods in this paper can provide a reference for the combined application of thermal and chemical stimulation technology in artificial reservoir reconstruction of hot dry rocks.
SUMMARY
Many natural hazards exhibit inverse power-law scaling of frequency and event size, or an exponential scaling of event magnitude (m) on a logarithmic scale, for example the Gutenberg–Richter ...law for earthquakes, with probability density function p(m) ∼ 10−bm. We derive an analytic expression for the bias that arises in the maximum likelihood estimate of b as a function of the dynamic range r. The theory predicts the observed evolution of the modal value of mean magnitude in multiple random samples of synthetic catalogues at different r, including the bias to high b at low r and the observed trend to an asymptotic limit with no bias. The situation is more complicated for a single sample in real catalogues due to their heterogeneity, magnitude uncertainty and the true b-value being unknown. The results explain why the likelihood of large events and the associated hazard is often underestimated in small catalogues with low dynamic range, for example in some studies of volcanic and induced seismicity.
SUMMARY
The International Seismological Centre (ISC) is a non‐governmental, non‐profit organization with the primary mission of producing the definitive account of the Earth's seismicity. The ISC ...Bulletin covers some 50 yr (1960–2011) of seismicity. The recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases, owing to the ever‐increasing number of stations worldwide. Similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the Earth, resulting in underestimated location uncertainties, and for unfavourable network geometries, location bias. Hence, the denser and more unbalanced the global seismic station coverage becomes, the less defensible is the assumption (that is the observations are independent), which is made by most location algorithms.
To address this challenge we have developed a new location algorithm for the ISC that accounts for correlated error structure, and uses all IASPEI standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations. In this paper we describe the new ISC locator, and present validation tests by relocating the ground truth events in the IASPEI Reference Event List, as well as by relocating the entire ISC Bulletin.
We show that the new ISC location algorithm provides small, but consistent location improvements, considerable improvements in depth determination and significantly more accurate formal uncertainty estimates. We demonstrate that the new algorithm, through the use of later phases and testing for depth resolution, considerably clusters event locations more tightly, thus providing an improved view of the seismicity of the Earth.
PDF
