Earthquake Science Center Seminars

Joan Gomberg, USGS

Like many of its partners, the USGS has recognized the tremendous opportunity for advancing earthquake science that subduction zones (SZs) offer, because of 1) the extraordinary diversity of SZ earthquakes and other natural phenomena they initiate and respond to, 2) the new perspectives inspired by required multi-disciplinary and international work, and 3) technological advances enabling offshore exploration. Participation of USGS personnel in SZ-relevant partners’ programs helps to ensure that the USGS fulfills its mandate to assess earthquake hazards and provide products useful for reducing risk. This mandate distinguishes USGS’s SZ activities, but also complements the goals of its many partners. USGS SZ science has largely been motivated and guided by its scientists, but with growing engagement at higher authoritative levels to reprogram and request new SZ-targeted resources. Although not a formal USGS project or program, SZ issues figure prominently in those that are, such as Powell Center projects focused on Cascadia megathrust recurrence and another on tsunami sources, the ShakeAlert Earthquake Early Warning project, the USGS-USAID Disaster Assistance programs, and a Risk Research and Applications Community of Practice. We present a few examples of forefront USGS SZ research, conducted in partnership with numerous collaborators. These include field and modeling studies of paleo-earthquake shaking proxies such as ‘fragile geologic features’ and onshore and offshore landslides, implementation of new seafloor geodetic measurement capabilities for event to coupling studies, terrestrial-quality resolution of submarine subsurface and surficial imaging and coring to test paradigms about recent and paleo-earthquakes, and much more!

Harry Lisabeth, Lawrence Berkeley National Laboratory

The behavior of the upper crust is controlled in large part by fractures. Fractures are the conduits of fluid flow, facilitate reactions and transport of mass, and mediate deformation large and small. Fractures are not static features, but rather are sensitive to the hydraulic, chemical and mechanical environment in which they are set. I'll present the results of a multimodal experimental study of the physical properties of fluid-saturated, fractured rock in response to changes in fluid chemistry and stress. Complementary measurements were made of changes in the fracture's physical structure to investigate the origins of the modified physical properties. The role of stress is shown to dominate the role of fluid composition, particularly at low effective stress, where nonlinear behavior becomes prevalent. I'll discuss the results in the context of geological engineering efforts, induced seismicity and the potential for remotely mapping stress in the subsurface.

Ben Holtzman, Lamont-Doherty Earth Observatory

Geothermal heat mining has the potential to become a significant contributor to a clean energy transition. However, significant problems must be overcome to safely and effectively engineer fluid pathways through fracture networks. Multiple approaches to unsupervised machine learning in seismology have the potential to help us discover complex and subtle patterns in acoustic signals. Physics-constrained learning, though not discussed here in detail, has the potential to associate patterns in multiple data types in time, micro- and macroscopic. Our aim is to be able to associate changes in a reservoir's acoustic signals with changes in its thermal-mechanical state and fracture processes. Towards this, we are building sets of analyses on active reservoirs and laboratory experiments. I will show results from two sets of (unpublished, ongoing) studies- first on a local section in the northwestern corner of The Geysers geothermal field in Northern CA, and second on a set of deformation experiments on basalt.

Ethan F. Williams, Seismological Laboratory, California Institute of Technology

In recent decades, the volume of research seismographic data from broadband and nodal arrays has exponentially outpaced the growth of structural and geotechnical data. With this revolution, new frontiers in “large-N” and “large-T” seismology have emerged, from monitoring ground water in sedimentary basins to high-resolution microseismic event location. By contrast, without continuous recordings and dense networks, current engineering practice for seismic structural health monitoring and post-earthquake damage assessment remains comparatively primitive. In this talk, I will make the case for big data in engineering seismology, highlighting the multi-scale complexity of structural vibrations in time and space, as well as the value of new technologies like distributed acoustic sensing (DAS).

First, I will focus on a 20-year record from a single strong-motion station (“large-T”). Since 2001, the Southern California Seismic Network has archived continuous waveform data from CI.MIK in Caltech Hall (formerly Millikan Library), a nine-story reinforced concrete building in Pasadena, CA. Simple spectral analysis of ambient vibrations reveals that the building's fundamental frequencies have gradually increased by 5.1% (E-W) and 2.3% (N-S), with larger long-term variability up to 9.7% (E-W) and 4.4% (N-S). This finding is unexpected, as previous analysis of forced vibration tests and strong-motion records has shown that between 1968 and 2003 the fundamental frequencies decreased by 22% (E-W) and 12% (N-S), largely attributed to minor structural damage and soil-structure system changes from earthquakes. Today, the building's apparent stiffness is comparable to what it was in 1986, before the Whittier Narrows earthquake, indicating significant passive healing. Using data from earthquakes and forced vibrations, I also document the building's nonlinear dynamic elasticity, which is characterized by a rapid softening (decrease in apparent frequencies) at the onset of strong motion, followed by a slower, log-linear recovery trend over the scale of minutes. Importantly, nonlinearity persists down to the amplitude of ambient vibrations, and there is no linear elastic regime.

Second, I will present two examples of DAS arrays recording structural vibrations in the far-field (“large -N”). Through rocking, displacement, and shearing of the foundation, structural vibrations driven by cyclic loading efficiently generate seismic waves. (1) With DAS data from seafloor power cables in the Belgian North Sea, I show that Scholte waves generated by wind turbine structural vibrations dominate the high-frequency ambient seismic field between 1-5 Hz. Utilizing array processing, these vibrations can be localized to individual turbines, opening the door for remote operational and structural health monitoring of an entire offshore wind park with a single DAS system. (2) Returning to Caltech Hall, forced vibration tests are similarly effective at exciting Rayleigh waves at the building’s natural frequencies. The Pasadena Array, a 37.5-km fiber-optic loop instrumented with DAS since 2018, records the building-generated seismic waves at 10-m resolution throughout the city. This combination of a repeatable 1-10 Hz controlled source with an ultra-dense recording array permits high-resolution seismic microzonation on the scale of a city block and time-lapse near-surface velocity monitoring.

Sara McBride, USGS Earthquake Science Center

The collection of online videos and imagery to use in disaster reconnaissance is increasing in frequency, due to accessibility of platforms and the ubiquitous nature of smartphones and recording devices. This presentation explores the processes, goals, and utility of online footage and imagery of geohazards (earthquakes, volcanoes, tsunamis, and landslides) to better understand human behavior. Searching techniques and processes have grown increasingly sophisticated and organized. This talk focuses on three case studies: the 2018 M7.1 Anchorage, 2021 M7.2 Nippes, Haiti earthquakes, as well as the historic Hunga Tonga–Hunga Haʻapai volcanic eruption generated atmospheric shockwaves recorded around the globe, as well as a damaging Pacific-wide tsunami. These videos offer a significant source of data about physical and event-related human behavior, given that little is currently known about human reaction to earthquakes as well as volcanic eruptions followed by tsunami of these magnitudes, as well as the physical phenomena. For the Hunga Tonga–Hunga Haʻapai collected more than 400 videos for the eruption and this data set offers novel information about people's reactions to the eruption and attendant tsunami obtained from 11 different nations throughout the Pacific Ocean basin. This collection provides potential insights into human behavior across cultures and national boundaries related to tsunami impacts. Two findings were of interest: one is that when presented with multiple eruption-related hazards, people were more likely to do nothing than take self-protective action, indicating the need for multi-hazard drills. Further, surprisingly, in our dataset the presence of children seemingly reduced the likelihood that protective action was taken, particularly in relation to the tsunami. These findings can inform future education and outreach efforts to assist in strengthening standardized protective actions for the impacted regions.

Matt Herman, CSU Bakersfield

Since 2020, three large magnitude earthquakes have occurred in the vicinity of the Shumagin Islands in Alaska: the 22 July 2020 Mw 7.8 megathrust event, the 19 October 2020 Mw 7.6 intra-slab strike-slip event and the 29 July 2021 Mw 8.2 megathrust event. The 2020 events occurred in the transition from high plate interface coupling east of the Shumagin Islands to low coupling near the Shumagin Islands, and our finite element models of coupling demonstrate that the slip behavior and kinematics of these events reflect this coupling transition. The 2021 Mw 8.2 megathrust earthquake occurred further to the east, rupturing a large part of the 10 November 1938 Mw 8.2 rupture zone. Slip models and aftershock activity suggest that nearly all the slip deficit that could accumulate since 1938 was recovered in the mainshock. We find using our coupling models that an uncoupled Shumagin Gap is most compatible with observations from the July 2021 earthquake. Although the Shumagin Gap appears to be uncoupled based on these earthquake sequences, the coupling situation up-dip of the 2021 earthquake remains enigmatic. Using our modeling setup, we explore implications for scenarios with various degrees of coupling on the shallow plate interface.

Robert Goldman, University of Illinois at Urbana-Champaign

The 2018 eruption of Kīlauea Volcano was the first natural hazard crisis event in which USGS social media communications played a major role in providing reliable, around-the-clock eruption information to publics. These communications complemented traditional channels including HVO’s website, radio and television broadcasts, newspaper articles, automated text or email alerts, and in-person community meetings. As part of my National Science Foundation Graduate Research Internship, I conducted two complementary investigations of these communications. First, I analyzed semi-structured in-person interviews conducted with residents of Hawai‘i in January 2020 to identify themes describing residents’ preferred sources, messengers, and channels of 2018 eruption information. I then analyzed the public comment threads of the @USGSVolcanoes Facebook page to determine how well dialogues between @USGSVolcanoes scientists and non-USGS users answered users’ eruption-related questions, addressed occurrences of misinformation, and benefitted users’ overall emotional state.

From this work, my collaborators and I identified the role that messengers’ perceived trustworthiness and credibility played in Hawai‘i residents’ reliance on information delivered by those messengers. We also learned that among the most frequently viewed @USGSVolcanoes Facebook posts, 73% of users’ questions were directly answered while 54% of comments containing misinformation were directly corrected or called out. Moreover, most users’ comments on the @USGSVolcanoes Facebook page contained positive emotions that reflect appreciation of the information provided by @USGSVolcanoes scientists. I conclude this talk by discussing the implications of our findings for planning future hazard communications in Hawai‘i and elsewhere.

Dorian Golriz, Scripps Institution of Oceanography

In the first part of this talk, I will present a new method to determine the earthquake’s coseismic time window using a combination of seismic and GNSS data. Current practice is to use daily GNSS positioning for static offsets determination and finite slip models. When using high-rate (1-5 Hz) GNSS positioning for this purpose, it is a common practice to take a single time window across all the affected stations (typically a few minutes). Since the postseismic phase starts immediately after the earthquake, in a continuous manner, these static offsets include early postseismic deformation that occurs minutes to hours after the earthquake. Here I show the differences between these offset estimates, and how they can affect coseismic slip models. In the second part the talk, I will show how we can use this coseismic time window to estimate earthquake magnitude for tsunami warning purposes. The Pacific Tsunami Warning Center (PTWC) uses a variety of tools to issue a tsunami warning based on the size and location of the earthquake. However, current methods that rely on seismic data alone suffer from magnitude saturation or not timely enough for coastal communities located closest to the earthquake’s rupture. The combination of GNSS and strong-motion data using a Kalman filter yields both broadband velocity and displacement waveforms that do not clip and are sensitive to the entire spectrum of ground motions. We can use this combination to rapidly determine earthquake magnitude. Replaying seismogeodetic data for a number of tsunamigenic earthquakes around the Pacific basin, we show that useful and reliable estimates can be obtained before the end of rupture. Additionally, our method does not rely on empirical relationships derived from historical earthquakes, making it suitable for local tsunami warning systems and shows promise for earthquake early warning.

Verónica Rodríguez Tribaldos, Lawrence Berkeley National Laboratory

In recent years, there has been growing interest in the seismological community for regional characterization and monitoring of subsurface processes at high temporal and spatial resolution, for applications as varied as fault identification, near-surface characterization or hydrological process monitoring. However, it has become evident that the utilization of permanent local or regional seismic networks for these purposes is limited, mostly due to sensor sparsity. The cost of running large-N, long-term temporary experiments is almost prohibitive. Distributed Acoustic Sensing (DAS) re-purposes telecommunication optical fibers as dense arrays of seismic sensors. This developing technology enables recording ground motions for long periods of time across long distances (10’s of km) at high spatial (~1 m) and temporal resolution at frequencies ranging from the mHz to the kHz. Recently, the deployment of this novel sensing technique on existing, unused fiber-optic cable networks, known as dark fiber, has offered an attractive alternative to classical seismological studies, as it facilitates acquisition of high-resolution data at regional scale. However, some challenges still exist before we can fully exploit the capabilities of this technology, the main challenge being the large data volumes derived from these several km-long, high density arrays. In this talk, we will show some examples of using dark fiber DAS for basin-scale characterization and monitoring using ambient seismic noise at a variety of scales in the Sacramento Valley, CA, and present preliminary observations from an ongoing experiment aiming at characterizing geothermal systems in the Imperial Valley, CA. We will also discuss some of the challenges associated with regional, high-resolution characterization using this novel technology and our recent attempts at developing effective data management and processing strategies.

Will Steinhardt, UC Santa Cruz Seismo Lab

Many systems in geophysics, including faults, ice sheets, and hill slopes, are predominantly stable, but become unstable catastrophically, with severe societal consequences when they do. However, the behaviors of these systems are often difficult to predict because they involve extreme spatial and temporal scales, accumulating stresses over decades or centuries, but nucleating failure processes at the micron-scale in fractions of a second leading to kilometers of deformation. In this talk, I will discuss how I utilize applied physics techniques to build scaled-down experiments to explore these complex problems in systems where a wide range of system properties can be tuned to make otherwise impossible observations. I will present two examples: First, using a scaled, transparent laboratory fault where slip at the interface can be directly imaged, I will show that slow slip events in our system follow earthquake-like scaling, and demonstrate how finite fault effects alter stress drop. Second, I will discuss how material heterogeneity leads to brittle fracture roughness, and show that the resultant morphology of a crack is, surprisingly, not dependent upon the details of the medium, but is controlled entirely by a single parameter: the probability to perturb the fracture front above a critical size to produce a step-like instability.