Tectonic faults fail through a spectrum of slip modes, ranging from slow aseismic creep to rapid slip during earthquakes. Understanding the seismic radiation emitted during these slip modes is key ...for advancing earthquake science and earthquake hazard assessment. In this work, we use laboratory friction experiments instrumented with ultrasonic sensors to document the seismic radiation properties of slow and fast laboratory earthquakes. Stick‐slip experiments were conducted at a constant loading rate of 8 μm/s and the normal stress was systematically increased from 7 to 15 MPa. We produced a full spectrum of slip modes by modulating the loading stiffness in tandem with the fault zone normal stress. Acoustic emission data were recorded continuously at 5 MHz. We demonstrate that the full continuum of slip modes radiate measurable high‐frequency energy between 100 and 500 kHz, including the slowest events that have peak fault slip rates <100 μm/s. The peak amplitude of the high‐frequency time‐domain signals scales systematically with fault slip velocity. Stable sliding experiments further support the connection between fault slip rate and high‐frequency radiation. Experiments demonstrate that the origin of the high‐frequency energy is fundamentally linked to changes in fault slip rate, shear strain, and breaking of contact junctions within the fault gouge. Our results suggest that having measurements close to the fault zone may be key for documenting seismic radiation properties and fully understanding the connection between different slip modes.
Plain Language Summary
Tectonic faults can slip rapidly within a few seconds producing intense ground shaking and radiating high‐frequency seismic energy, or they can slip slowly over much longer time scales and emanate weak seismic signals. Understanding the seismic properties of slow and fast earthquakes is a key goal in earthquake science and could have important implications for earthquake hazard. Here, we use laboratory friction experiments instrumented with ultrasonic transducers and document systematic variations in seismic properties for slow and fast laboratory earthquakes. Our data show that both slow and fast laboratory earthquakes radiate measurable high‐frequency energy. Fault slip rate plays a key role in modulating high‐frequency energy and we propose that the origin of this high‐frequency energy originates from the breaking of grain contacts. The high‐frequency characteristics of slow and fast lab earthquakes seem to follow different scaling relationships, which could have important implications for illuminating the connections between slow and fast earthquakes in natural fault systems.
Key Points
We document seismic radiation properties of laboratory earthquakes for a spectrum of failure modes from stable sliding to fast stick‐slip
The full spectrum of labquake failure modes radiate measurable high‐frequency energy between 100 and 500 kHz
High‐frequency energy in slow and fast laboratory earthquakes scales systematically with fault slip rate
Big Data Seismology Arrowsmith, S. J.; Trugman, D. T.; MacCarthy, J. ...
Reviews of geophysics (1985),
June 2022, Letnik:
60, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The discipline of seismology is based on observations of ground motion that are inherently undersampled in space and time. Our basic understanding of earthquake processes and our ability to resolve ...4D Earth structure are fundamentally limited by data volume. Today, Big Data Seismology is an emergent revolution involving the use of large, data‐dense inquiries that is providing new opportunities to make fundamental advances in these areas. This article reviews recent scientific advances enabled by Big Data Seismology through the context of three major drivers: the development of new data‐dense sensor systems, improvements in computing, and the development of new types of techniques and algorithms. Each driver is explored in the context of both global and exploration seismology, alongside collaborative opportunities that combine the features of long‐duration data collections (common to global seismology) with dense networks of sensors (common to exploration seismology). The review explores some of the unique challenges and opportunities that Big Data Seismology presents, drawing on parallels from other fields facing similar issues. Finally, recent scientific findings enabled by dense seismic data sets are discussed, and we assess the opportunities for significant advances made possible with Big Data Seismology. This review is designed to be a primer for seismologists who are interested in getting up‐to‐speed with how the Big Data revolution is advancing the field of seismology.
Plain Language Summary
Seismology is the scientific discipline by which vibrational waves that travel through the Earth are used to study a range of natural processes, from the structure and layering of the subsurface to the dynamics of earthquake rupture. Long propelled by advances in instrumentation and the availability of waveform observations, seismology has entered an era of Big Data where new opportunities come hand in hand with new challenges. This review article gives an overview of recent scientific advances powered by Big Data Seismology, along with emerging trends, potential challenges, and future opportunities. The review encompasses a range of subjects from seismic imaging and earthquake source physics to education and outreach, and is designed to be a jumping off point for readers interested in how big data is changing the face of seismology research.
Key Points
Big Data Seismology is an emergent subdiscipline that uses “big data” inquiries to explore fundamental science questions in seismology
Three drivers of Big Data Seismology are the growth of large data volumes, the development of new algorithms, and advances in computing
Big Data Seismology is being applied to study earthquakes, to better resolve Earth structure, and to open new frontiers in seismology
Foreshocks have been recorded as preceding less than half of all mainshock earthquakes. These observations are difficult to reconcile with laboratory earthquake experiments and theoretical models of ...earthquake nucleation, which both suggest that foreshock activity should be nearly ubiquitous. In this work, we use a state-of-the-art, high-resolution earthquake catalog to study foreshock sequences of magnitude M4 and greater mainshocks in southern California from 2008–2017. This highly complete catalog provides a new opportunity to examine smaller magnitude precursory seismicity. Seventy-two percent of mainshocks within this catalog are preceded by foreshock activity that is significantly elevated compared to the local background seismicity rate. Foreshock sequences vary in duration from several days to weeks, with a median of 16.6 days. The results imply that foreshock occurrence in nature is more prevalent than previously thought and that our understanding of earthquake nucleation may improve in tandem with advances in our ability to detect small earthquakes.
We study the physics of dynamically triggered tectonic tremor by applying a brittle‐ductile friction model in which we conceptualize the tremor source as a rigid block subject to driving and ...frictional forces. To simulate dynamic triggering of tremor, we apply a stress perturbation that mimics the surface waves of remote earthquakes. The tectonic and wave perturbation stresses define a phase space that demonstrates that both the timing and amplitude of the dynamic perturbations control the fundamental characteristics of triggered tremor. Tremor can be triggered instantaneously or with a delayed onset if the dynamic perturbation significantly alters the frictional state of the tremor source.
Key Points
Dynamic triggering of tremor is simulated using a brittle‐ductile friction model
Triggering potential depends on both perturbation amplitude and tectonic stress
Delayed‐onset triggering of seismicity can occur due to nonlinear fault friction
•We observe tidal modulation of earthquakes within the Coso geothermal field.•The earthquakes preferentially occur near times of maximum tensile tidal stress.•Tidal triggering occurs close to the ...edge of the area of new active production.•Spatial patterns of tidal triggering are more consistent than remote triggering.
Studying the seismicity triggering response of fault systems to periodic stress fluctuations can improve our understanding of earthquake nucleation, rupture failure processes, and local stress states. Geothermal fields are well known to be susceptible to triggering, as the injection and extraction activities change the local stress and fluid flow conditions. Here, we examine the modulation of earthquakes by Earth tides within California's Coso geothermal field (CGF) and its vicinity. To maximize our resolution to detect modulation of small earthquakes, we take advantage of the new Quake Template Matching catalog in southern California, which has nearly twice as many events in the Coso region as the standard catalog and is complete down to about magnitude 0.3. We observe strong tidal triggering of earthquakes within the CGF, even though the fluctuations of tidal stresses are small (∼2 kPa). The tidally-triggered earthquakes tend to occur near the time of maximum tensile tidal stress. The signal is strongest near the edges of the zone of new production wells, suggesting fluid pressure gradients encourages triggering at tidal periods.
We study the ability of statistical tests to identify nonrandom features of earthquake catalogs, with a focus on the global earthquake record since 1900. We construct four types of synthetic data ...sets containing varying strengths of clustering, with each data set containing on average 10,000 events over 100 years with magnitudes above M = 6. We apply a suite of statistical tests to each synthetic realization in order to evaluate the ability of each test to identify the sequences of events as nonrandom. Our results show that detection ability is dependent on the quantity of data, the nature of the type of clustering, and the specific signal used in the statistical test. Data sets that exhibit a stronger variation in the seismicity rate are generally easier to identify as nonrandom for a given background rate. We also show that we can address this problem in a Bayesian framework, with the clustered data sets as prior distributions. Using this new Bayesian approach, we can place quantitative bounds on the range of possible clustering strengths that are consistent with the global earthquake data. At M = 7, we can estimate 99th percentile confidence bounds on the number of triggered events, with an upper bound of 20% of the catalog for global aftershock sequences, with a stronger upper bound on the fraction of triggered events of 10% for long‐term event clusters. At M = 8, the bounds are less strict due to the reduced number of events. However, our analysis shows that other types of clustering could be present in the data that we are unable to detect. Our results aid in the interpretation of the results of statistical tests on earthquake catalogs, both worldwide and regionally.
Key Points
We apply statistical tests to synthetic clustered earthquake catalogs
Success of a test depends on the test, type of clustering, and quantity of data
The fraction of triggered global M = 7 events is below 20% for aftershocks
Searching for hidden earthquakes in Southern California Ross, Zachary E.; Trugman, Daniel T.; Hauksson, Egill ...
Science (American Association for the Advancement of Science),
04/2019, Letnik:
364, Številka:
6442
Journal Article
Recenzirano
Earthquakes follow a well-known power-law size relation, with smaller events occurring much more often than larger events. Earthquake catalogs are thus dominated by small earthquakes, yet still ...missing a much larger number of even smaller events caused by signal fidelity issues. To overcome these limitations, we applied a template matching detection technique to the entire waveform archive of the regional seismic network in southern California. Furthermore this effort resulted in a catalog with 1.81 million earthquakes, a factor of 10 increase, which provides important new insights into the geometry of fault zones at depth, foreshock behavior and nucleation processes, and earthquake triggering mechanisms. The extraordinary detail resolved in this type of catalog will facilitate a new generation of analyses of earthquakes and faults.
Laboratory earthquake experiments provide important observational constraints for our understanding of earthquake physics. Here we leverage continuous waveform data from a network of piezoceramic ...sensors to study the spatial and temporal evolution of microslip activity during a shear experiment with synthetic fault gouge. We combine machine learning techniques with ray theoretical seismology to detect, associate, and locate tens of thousands of microslip events within the gouge layer. Microslip activity is concentrated near the center of the system but is highly variable in space and time. While microslip activity rate increases as failure approaches, the spatiotemporal evolution can differ substantially between stick-slip cycles. These results illustrate that even within a single, well-constrained laboratory experiment, the dynamics of earthquake nucleation can be highly complex.
Plants influence the atmosphere through fluxes of carbon, water and energy, and can intensify drought through land–atmosphere feedback effects. The diversity of plant functional traits in forests, ...especially physiological traits related to water (hydraulic) transport, may have a critical role in land–atmosphere feedback, particularly during drought. Here we combine 352 site-years of eddy covariance measurements from 40 forest sites, remote-sensing observations of plant water content and plant functional-trait data to test whether the diversity in plant traits affects the response of the ecosystem to drought. We find evidence that higher hydraulic diversity buffers variation in ecosystem flux during dry periods across temperate and boreal forests. Hydraulic traits were the predominant significant predictors of cross-site patterns in drought response. By contrast, standard leaf and wood traits, such as specific leaf area and wood density, had little explanatory power. Our results demonstrate that diversity in the hydraulic traits of trees mediates ecosystem resilience to drought and is likely to have an important role in future ecosystem–atmosphere feedback effects in a changing climate.
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