Minimal damage from the Julian earthquake should result in maximum earthquake preparedness efforts.

ABSTRACT The Rose Canyon fault is the southern extension of the larger Newport–Inglewood–Rose Canyon fault system, which represents a major structural boundary in the Inner Continental Borderland (ICB) offshore of southern California. Ten to fifteen percent of total plate boundary motion in southern California is thought to be accommodated by the faults of the ICB, but the exact distribution of slip is uncertain. With an onshore segment, the Rose Canyon fault offers an opportunity to measure the slip rate using traditional geodetic methods. In this study, we use Global Positioning System (GPS) surface velocities from a combined campaign and continuous GPS network to constrain elastic models of the Rose Canyon fault. We then compare the observed surface velocities with proposed conceptual models of regional fault connections that facilitate the transfer of slip into the Rose Canyon fault to assess how well the observations are explained by the models. The results of elastic half-space models suggest that the Rose Canyon fault may be slipping toward the higher end of geologic estimates, with the preferred model indicating a slip rate of 2.4 ± 0.5 mm/yr. Although limited in terms of near-fault benchmarks, we find an improved model fit using an asymmetrical elastic half-space model and a higher slip rate, suggesting a potential rheological contrast across the Rose Canyon fault, similar to observations from the northern Newport–Inglewood fault segments. Observed GPS surface velocities, background seismicity, and gravity anomalies south of San Diego Bay point toward a more easterly trace for the Rose Canyon fault, suggesting a possible connection with the San Miguel–Vallecitos fault system. Such a connection could increase the potential rupture lengths of future earthquakes and have important consequences for regional seismic hazards.

Correction| January 10, 2024 Erratum to Reply to "Comment on 'Sources of Long‐Range Anthropogenic Noise in Southern California and Implications for Tectonic Tremor Detection' by Asaf Inbal, Tudor Cristea‐Platon, Jean‐Paul Ampuero, Gregor Hillers, Duncan Agnew, and Susan E. Hough" by Allie Hutchison, Yijian Zhou, and Abhijit Ghosh Asaf Inbal; Asaf Inbal * 1Department of Geophysics, Tel Aviv University, Tel Aviv, Israel *Corresponding author: asafinbal@tauex.tau.ac.il https://orcid.org/0000-0001-8848-7279 Search for other works by this author on: GSW Google Scholar Tudor Cristea‐Platon; Tudor Cristea‐Platon 2Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A. https://orcid.org/0000-0001-8268-4693 Search for other works by this author on: GSW Google Scholar Jean‐Paul Ampuero; Jean‐Paul Ampuero 3Université Côte d'Azur, IRD, CNRS, Observatoire de la Côte d'Azur, Géoazur, France https://orcid.org/0000-0002-4827-7987 Search for other works by this author on: GSW Google Scholar Gregor Hillers; Gregor Hillers 4Institute of Seismology, University of Helsinki, Helsinki, Finland https://orcid.org/0000-0003-2341-1892 Search for other works by this author on: GSW Google Scholar Duncan Agnew Duncan Agnew 5Scripps Institution of Oceanography, University of California, San Diego, California, U.S.A. https://orcid.org/0000-0002-2360-7783 Search for other works by this author on: GSW Google Scholar Author and Article Information Asaf Inbal https://orcid.org/0000-0001-8848-7279 * 1Department of Geophysics, Tel Aviv University, Tel Aviv, Israel Tudor Cristea‐Platon https://orcid.org/0000-0001-8268-4693 2Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A. Jean‐Paul Ampuero https://orcid.org/0000-0002-4827-7987 3Université Côte d'Azur, IRD, CNRS, Observatoire de la Côte d'Azur, Géoazur, France Gregor Hillers https://orcid.org/0000-0003-2341-1892 4Institute of Seismology, University of Helsinki, Helsinki, Finland Duncan Agnew https://orcid.org/0000-0002-2360-7783 5Scripps Institution of Oceanography, University of California, San Diego, California, U.S.A. *Corresponding author: asafinbal@tauex.tau.ac.il Publisher: Seismological Society of America First Online: 10 Jan 2024 Online ISSN: 1943-3573 Print ISSN: 0037-1106 © Seismological Society of America Bulletin of the Seismological Society of America (2024) 114 (2): 1182–1183. https://doi.org/10.1785/0120230133 Article history First Online: 10 Jan 2024 Connected Content Errata: Reply to "Comment on 'Sources of Long‐Range Anthropogenic Noise in Southern California and Implications for Tectonic Tremor Detection' by Asaf Inbal, Tudor Cristea‐Platon, Jean‐Paul Ampuero, Gregor Hillers, Duncan Agnew, and Susan E. Hough" by Allie Hutchison, Yijian Zhou, and Abhijit Ghosh Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Asaf Inbal, Tudor Cristea‐Platon, Jean‐Paul Ampuero, Gregor Hillers, Duncan Agnew; Erratum to Reply to "Comment on 'Sources of Long‐Range Anthropogenic Noise in Southern California and Implications for Tectonic Tremor Detection' by Asaf Inbal, Tudor Cristea‐Platon, Jean‐Paul Ampuero, Gregor Hillers, Duncan Agnew, and Susan E. Hough" by Allie Hutchison, Yijian Zhou, and Abhijit Ghosh. Bulletin of the Seismological Society of America 2024;; 114 (2): 1182–1183. doi: https://doi.org/10.1785/0120230133 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Because of a printing error, the x‐axis labels are missing from figures 8–10 in the reply article of Inbal et al. (2023) to the comment article of Hutchison et al. (2023). This erratum contains the corrected figures labeled here as Figures 1–3. The authors acknowledge that there are no conflicts of interest recorded. View Original Article You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The historical association of time with the rotation of Earth has meant that Coordinated Universal Time (UTC) closely follows this rotation 1 . Because the rotation rate is not constant, UTC contains discontinuities (leap seconds), which complicates its use in computer networks 2 . Since 1972, all UTC discontinuities have required that a leap second be added 3 . Here we show that increased melting of ice in Greenland and Antarctica, measured by satellite gravity 4 , 5 , has decreased the angular velocity of Earth more rapidly than before. Removing this effect from the observed angular velocity shows that since 1972, the angular velocity of the liquid core of Earth has been decreasing at a constant rate that has steadily increased the angular velocity of the rest of the Earth. Extrapolating the trends for the core and other relevant phenomena to predict future Earth orientation shows that UTC as now defined will require a negative discontinuity by 2029. This will pose an unprecedented problem for computer network timing and may require changes in UTC to be made earlier than is planned. If polar ice melting had not recently accelerated, this problem would occur 3 years earlier: global warming is already affecting global timekeeping.

In 2022, the Hunga volcano eruption in Tonga generated atmospheric pressure waves that propagated globally and produced tsunamis in all the world's oceans. The largest pressure wave, with an amplitude of several hundred pascals, is the Lamb wave. Standard Lamb wave models, incorporating the sound-speed as a function of temperature, satisfactorily explain observations in the near-field but not in the far-field. We show that an augmented Lamb wave model that includes the effects of wind and topography accurately reproduces the wavefronts observed by satellites and barometers, including those close to the antipode. Winds, first suggested to explain the travel times of Lamb waves from Krakatau in 1883, are now shown to also play a major role in shaping their waveforms; temperature and topography play smaller, but still detectable, roles. Our augmented model provides a significant advance for the development of early warning and hazard assessments for the meteotsunamis these waves produce. The January 2022 explosive eruption of the Hunga volcano in Tonga produced a pressure wave (of a type known as a Lamb wave) in the atmosphere, which was detected worldwide. This wave circled the Earth more than once, and generated tsunami in unexpected times and places. We have derived a mathematical description that allows us to quickly and accurately model the observations of this atmospheric wave. The description includes the effects of winds, temperature, and topography. The wave modeled using this description reproduces satellite and ground observations much better than simpler models, notably the complex pattern of the wave near the antipode of the eruption. Our model clearly identifies global winds as the crucial influence on global-scale Lamb-wave propagation, and provides modeling tools for possible future occurrences of such waves and the global tsunamis created by them. A augmented model is proposed to simulate the propagation of planetary scale Lamb waves, incorporating wind, temperature and topographyWinds play a primary role shaping Lamb waves in the far field, especially near the antipode of the sourceThe augmented Lamb wave model will help better assess far-field volcanic tsunami hazards

I discuss how much attention different earthquakes get in the scientific and nonscientific literature. For the former, all earthquakes above magnitude 7.5 appear in a scientific article, and the number of articles tends to increase with magnitude. For the latter, most shocks, even if damaging, become largely forgotten in a few decades, though some, such as the 1906 San Francisco earthquake, live on in popular memory.

Accurate time measurement is a crucial element of seismic data collection. For data collected before the 1980s and especially before 1960, the technologies involved are no longer familiar to most researchers. I outline how reliable time has been obtained for seismology and describe the histories of master clocks, local clocks, time transfer, time comparison, and uniform motion for visual recording. A compendium of station data for 1921 gives a snapshot of early seismological timekeeping. I present an overview of subsequent developments, with suggestions on how to weight observed times using descriptions of the timing system used.

Tidal fluctuations in gravity will affect the period of a pendulum and hence the timekeeping of any such clock that uses one. Since pendulum clocks were, until the 1940s, the best timekeepers available, there has been interest in seeing if tidal effects could be observed in the best performing examples of these clocks. The first such observation was in 1929, before gravity tides were measured with spring gravimeters; at the time of the second (1940–1943), such gravimeters were still being developed. Subsequent observations, having been made after pendulum clocks had ceased to be the best available timekeepers and after reliable gravimeter measurements of tides, have been more of an indication of clock quality than a contribution to our knowledge of tides. This paper describes the different measurements and revisits them in terms of our current knowledge of Earth tides. Doing so shows that clock-based systems, though noisier than spring gravimeters, were an early form of an absolute gravimeter that could indeed observe Earth tides.

We study temporal changes of seismic velocity (dv/v) in the crust around the central section of the San Jacinto fault zone (SJFZ), Southern California. Focusing on a 200‐day‐long period around April 2010, our analysis resolves two tens‐of‐days‐long successive episodes of reduced velocities that are compatible with signals from the long base strainmeter at the Piñon Flat Observatory. The imaged dv/v sequences are proxies for evolving material properties in the crust surrounding the SJFZ. The temporal and the spatial coincidence of the observed dv/v patterns with the occurrence of two proposed creep episodes suggest that the relative velocity changes reflect the response to deep creep events that follow the M7.2 El Mayor‐Cucapah earthquake and the M5.4 Collins Valley earthquake that occurred 94 days later on the San Jacinto fault. The main slip during the creep events was proposed to occur below 10‐km depth. Wavefield properties suggest sensitivity to medium changes above this source zone, in the top 10 km. The distribution of the obtained dv/v reductions shows a strong difference between large values to the west of the SJFZ and significantly smaller amplitudes to the east. The similarity to the seasonal velocity change pattern implies that the results are likely controlled by the contrast of mechanical properties across the fault, such as fault‐perpendicular shear modulus variations. Our analysis extends the spectrum of methods that can be used to study earthquake interaction, fault zone rheology and dynamics, triggering, and the interplay between creep episodes and earthquakes.

ABSTRACT It has recently been argued that the large mid-continental earthquakes near New Madrid, Missouri, were mostly forgotten soon after they occurred in 1811–1812, in large part because the records available (historical narratives) were qualitative and taken to be unreliable. This obscurity is supposed to have lasted until the 1970s or later, when scientific study of the earthquakes resumed, and their significance for hazard became recognized. An examination of a wider range of sources suggests that while the memory of these earthquakes may have suffered the natural fate of most historical events, and faded in the broader population, the professional community of seismologists and engineers never lost sight of these earthquakes. Increased research in the 1970s on seismic hazards in mid-continental North America happened because of new opportunities created by funding and new technology, not a sudden remembering. Nor were these earthquakes neglected because seismology turned from description using descriptive measures (intensity of shaking) to analysis using instrumental data: intensity data were collected and used throughout the twentieth century.

The resonance associated with the ellipticity of the core-mantle boundary is usually measured with observations of either the Earth’s nutations, or of tidal gravity, strain, or tilt. But, improbably, it can also be seen in a dataset collected and processed with older and simpler technologies: the harmonic constants for the ocean tides. One effect of the resonance is to decrease the ratio of the amplitude of the P1 constituent to the amplitude of the K1 constituent to 0.96 of the ratio in the equilibrium tidal potential. The compilation of ocean-tide harmonic constants prepared by the International Hydrographic Bureau between 1930 and 1980 shows considerable scatter in this ratio; however, if problematic stations and regions are removed, this dataset clearly shows a decreased ratio. While these data apply only a weak constraint to the frequency of the resonance, they also show that the effect could have been observed long before it actually was.

The unique instrument setting at the Pinon Flat Observatory in California is used to simultaneously measure 10 out of the 12 components, completely describing the seismic-wave field. We compare the direct measurements of rotation and strain for the 13 September 2015 M-w 6.7 Gulf of California earthquake with array-derived observations using this configuration for the first time. In general, we find a very good fit between the observations of the two measurements with cross-correlation coefficients up to 0.99. These promising results indicate that the direct and array-derived measurements of rotation and strain are consistent. For the array-based measurement, we derived a relation to estimate the frequency range within which the array-derived observations provide reliable results. This relation depends on the phase velocity of the study area and the calibration error, as well as on the size of the array.

Abstract The relationship (scaling) between scalar moment, M0, and duration, T, potentially provides key constraints on the physics governing fault slip. The prevailing interpretation of M0‐T observations proposes different scaling for fast (earthquakes) and slow (mostly aseismic) slip populations and thus fundamentally different driving mechanisms. We show that a single model of slip events within bounded slip zones may explain nearly all fast and slow slip M0‐T observations, and both slip populations have a change in scaling, where the slip area growth changes from 2‐D when too small to sense the boundaries to 1‐D when large enough to be bounded. We present new fast and slow slip M0‐T observations that sample the change in scaling in each population, which are consistent with our interpretation. We suggest that a continuous but bimodal distribution of slip modes exists and M0‐T observations alone may not imply a fundamental difference between fast and slow slip.

We present alternative source models for very low frequency (VLF) events, previously inferred to be radiation from individual slow earthquakes that partly fill the period range between slow slip events lasting thousands of seconds and low-frequency earthquakes (LFE) with durations of tenths of a second. We show that VLF events may emerge from bandpass filtering a sum of clustered, shorter duration, LFE signals, believed to be the components of tectonic tremor. Most published studies show VLF events occurring concurrently with tremor bursts and LFE signals. Our analysis of continuous data from Costa Rica detected VLF events only when tremor was also occurring, which was only 7% of the total time examined. Using analytic and synthetic models, we show that a cluster of LFE signals produces the distinguishing characteristics of VLF events, which may be determined by the cluster envelope. The envelope may be diagnostic of a single, dynamic, slowly slipping event that propagates coherently over kilometers or represents a narrowly band-passed version of nearly simultaneous arrivals of radiation from slip on multiple higher stress drop and/or faster propagating slip patches with dimensions of tens of meters (i.e., LFE sources). Temporally clustered LFE sources may be triggered by single or multiple distinct aseismic slip events or represent the nearly simultaneous chance occurrence of background LFEs. Given the nonuniqueness in possible source durations, we suggest it is premature to draw conclusions about VLF event sources or how they scale.