Seismological Community Research Articles

Measuring Group Velocity in Seismic Noise Correlation Studies Based on Phase Coherence and Resampling Strategies

Seismic noise cross correlation studies are of increasing importance in the seismological research community due to the ubiquity of noise sources and advances on how to use the seismic noise wave field for structural imaging and monitoring purposes. Stacks of noise cross correlations are now routinely used to extract empirical Green’s functions between station pairs. In regional and global scale studies, mostly surface waves are extracted due to their dominance in seismic noise wave fields. Group arrival times measured from the time-frequency representation of frequency dispersive surface waves are further used in tomographic inversions to image seismic structure. Often, the group arrivals are not clearly identified or ambiguous depending on the signal and noise characteristics. Here, we present a procedure to robustly measure group velocities using the time-frequency domain phase-weighted stack (PWS) combined with data resampling and decision strategies. The time-frequency PWS improves signal extraction through incoherent signal attenuation during the stack of the noise cross correlations. Resampling strategies help to identify signals robust against data variations and to assess their errors. We have gathered these ingredients in an algorithm where the decision strategies and tuning parameters are reduced for semiautomated processing schemes. Our numerical and field data examples show a robust assignment of surface-wave group arrivals. The method is computational efficient thanks to an implementation based on pseudoanalytic frames of wavelets and enables processing large amounts of data.

Appraising the PSHA Earthquake Source Models of Japan, New Zealand, and Taiwan

ABSTRACT Earthquake‐hazard models are one of the major contributions provided by the seismological community to tangibly support disaster risk reduction policies at a national level. Although the societal impact of hazard analyses can be huge, the development of models remains a scientific activity developed within frameworks that have a strong national emphasis and partial international recognition. However, broad acceptability of hazard models is a key aspect for achieving authoritativeness and a prerequisite for warranting that their construction is completed using well‐recognized methodologies. As part of an enduring international collaboration between leading organizations operating in the hazard and risk fields in Japan, New Zealand, Taiwan, and the Global Earthquake Model initiative, we discuss the main characteristic of the earthquake source models—as implemented for the OpenQuake engine—used for the calculation of the most recent national seismic‐hazard maps of these three countries. Particular emphasis is placed on comparing the various modeling options adopted in the different tectonic regions, on emphasizing commonalities, and on discussing the most controversial modeling solutions. Despite the many connections from a seismotectonic point of view between the three countries, the comparison highlights different modeling choices for the various tectonic regions, which constitute a spectrum of possible epistemic uncertainties, as well as modeling issues that could be collectively explored in future phases of this international collaboration.

Investigating Triggering of the Aftershocks of the 2014 Napa Earthquake

Abstract The occurrence of the M w 6.0 South Napa California earthquake, on 24 August 2014 at 03:20 a.m. local time, triggered discussion in the seismological community about the level of damage associated with such a moderate‐magnitude event and about the geometry and orientation of the causative fault. In addition, coulomb static stress change mapping does not seem to be able to fully explain near‐source aftershock distribution. Here, we find clear evidence of a north‐northwest source directivity from the analysis of the spatial distribution of peak ground motion. The area of the highest values of the estimated peak dynamic strain field, computed accounting for fault extent and source directivity, agrees with the near‐source aftershock distribution. This might suggest that, in addition to coulomb static stress change, dynamic strain also contributed to the triggering of near‐source Napa earthquake aftershocks. The approach used here might be useful to identify areas likely prone to aftershock occurrence.

A scheme to set preferred magnitudes in the ISC Bulletin

One of the main purposes of the International Seismological Centre (ISC) is to collect, integrate and reprocess seismic bulletins provided by agencies around the world in order to produce the ISC Bulletin. This is regarded as the most comprehensive bulletin of the Earth’s seismicity, and its production is based on a unique cooperation in the seismological community that allows the ISC to complement the work of seismological agencies operating at global and/or local-regional scale. In addition, by using the seismic wave measurements provided by reporting agencies, the ISC computes, where possible, its own event locations and magnitudes such as short-period body wave m b and surface wave M S . Therefore, the ISC Bulletin contains the results of the reporting agencies as well as the ISC own solutions. Among the most used seismic event parameters listed in seismological bulletins, the event magnitude is of particular importance for characterizing a seismic event. The selection of a magnitude value (or multiple ones) for various research purposes or practical applications is not always a straightforward task for users of the ISC Bulletin and related products since a multitude of magnitude types is currently computed by seismological agencies (sometimes using different standards for the same magnitude type). Here, we describe a scheme that we intend to implement in routine ISC operations to mark the preferred magnitudes in order to help ISC users in the selection of events with magnitudes of their interest.

Operational (Short‐Term) Earthquake Loss Forecasting in Italy

Abstract The seismological community is currently developing operational earthquake forecasting (OEF) systems that aim to estimate the seismicity in an area of interest, based on continuous ground‐motion recording by seismic networks; the seismicity may be expressed, for example, in terms of rates of events exceeding a certain magnitude threshold in a short period of time (days to weeks). OEF possibly may be used for short‐term seismic risk management in regions affected by seismic swarms only if its results may be the input to compute, in a probabilistically sound manner, consequence‐based risk metrics. The present article reports on the feasibility of short‐term risk assessment, or operational earthquake loss forecasting (OELF), in Italy. The approach is that of performance‐based earthquake engineering, in which the loss rates are computed by means of hazard, vulnerability, and exposure. The risk is expressed in terms of individual and regional measures, which are based on short‐term macroseismic intensity (or ground‐motion intensity) hazard. The vulnerability of the built environment relies on damage probability matrices empirically calibrated for Italian structural classes; the exposure is represented in terms of buildings per vulnerability class and occupants per building typology. All vulnerability and exposure data are at the municipality scale. The developed procedure, which is virtually independent of the seismological model used, is implemented in an experimental OELF system that continuously processes OEF information to produce nationwide risk maps applying to the week after the OEF data release. This is illustrated by a retrospective application to the 2012 Pollino (southern Italy) seismic sequence, which provides insights on the capabilities of the system and on the impact of the methodology currently used for OEF in Italy on short‐term risk assessment.

Improvements in Data Quality, Integration and Reliability: New Developments at the IRIS DMC

Abstract. With the support of the US National Science Foundation (NSF) and on behalf of the international seismological community, IRIS developed a Data Management Center (DMC; Ahern, 2003) that has for decades acted as a primary resource for seismic networks wishing to make their data broadly available, as well as a significant point of access for researchers and monitoring agencies worldwide that wish to access high quality data for a variety of purposes. Recently IRIS has taken significant new steps to improve the quality of and access to the services of the IRIS DMC. This paper highlights some of the current new efforts being undertaken by IRIS. The primary topics include (1) steps to improve reliability and consistency of access to IRIS data resources, (2) a comprehensive new approach to assessing the quality of seismological and other data, (3) working with international partners to federate seismological data access services, and finally (4) extensions of the federated concept to extend data access to data from other geoscience domains.

Anton M. Dainty (1942-2014)

Obituary| December 03, 2014 Anton M. Dainty (1942–2014) M. Nafi Toksoz; M. Nafi Toksoz The authors would like to acknowledge Eystein Husebye, Andy Michael, and Keith McLaughlin for remembrances that reminded us of all the ways Anton contributed to the seismological research community. Search for other works by this author on: GSW Google Scholar Rick Schult; Rick Schult The authors would like to acknowledge Eystein Husebye, Andy Michael, and Keith McLaughlin for remembrances that reminded us of all the ways Anton contributed to the seismological research community. Search for other works by this author on: GSW Google Scholar Katharine Kadinsky‐Cade Katharine Kadinsky‐Cade The authors would like to acknowledge Eystein Husebye, Andy Michael, and Keith McLaughlin for remembrances that reminded us of all the ways Anton contributed to the seismological research community. Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2015) 86 (1): 13–14. https://doi.org/10.1785/0220140217 Article history first online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. Nafi Toksoz, Rick Schult, Katharine Kadinsky‐Cade; Anton M. Dainty (1942–2014). Seismological Research Letters 2014;; 86 (1): 13–14. doi: https://doi.org/10.1785/0220140217 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 SocietySeismological Research Letters Search Advanced Search Dr. Anton M. Dainty, a seismologist with a broad range of contributions, passed away on 15 August 2014, at his home in Waltham, Massachusetts. He published nearly 100 papers on seismic‐wave propagation, scattering, Earth structure, and lunar seismology and was a major scientific guide for the global field of nuclear monitoring seismology from 1996 to 2010. He had the distinction of making major contributions to both terrestrial and lunar seismology. Anton was born on 26 December 1942 in the United Kingdom and did his undergraduate studies in physics at the University of Edinburgh. His Ph.D. in marine geophysics at Dalhousie... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Schmandt Receives 2013 Keiiti Aki Young Scientist Award: Response

I appreciate Karen's generous words, and I am sincerely honored to receive this year's Aki Award. I would like to acknowledge that my research has been enabled by excellent mentors and colleagues and by a unique community of scientists. I was particularly lucky to wander into Gene Humphrey's office as a first‐year graduate student with a curiosity about western U.S. tectonics and seismology. Gene always matched my energy and enthusiasm and allowed me to find my path. Later, as a postdoc, I benefited from a similarly flexible and supportive environment in the Seismo Lab at Caltech. I also feel fortunate to be part of the seismology community. It is a special community that will strive to collect a world‐class data set, such as the EarthScope seismic data, and then openly put those data in the hands of any eager scientist. This unselfish and open‐minded perspective is a great motivation for me, and I expect it is for many young scientists. I am excited for the future as a member of the seismology community.

On numerical earthquake prediction

Can earthquakes be predicted? How should people overcome the difficulties encountered in the study of earthquake prediction? This issue can take inspiration from the experiences of weather forecast. Although weather forecasting took a period of about half a century to advance from empirical to numerical forecast, it has achieved significant success. A consensus has been reached among the Chinese seismological community that earthquake prediction must also develop from empirical forecasting to physical prediction. However, it is seldom mentioned that physical prediction is characterized by quantitatively numerical predictions based on physical laws. This article discusses five key components for numerical earthquake prediction and their current status. We conclude that numerical earthquake prediction should now be put on the planning agenda and its roadmap designed, seismic stations should be deployed and observations made according to the needs of numerical prediction, and theoretical research should be carried out.

A New ISC Service: The Bibliography of Seismic Events

Research Article| March 01, 2014 A New ISC Service: The Bibliography of Seismic Events D. Di Giacomo; D. Di Giacomo International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar D. A. Storchak; D. A. Storchak International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar N. Safronova; N. Safronova International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar P. Ozgo; P. Ozgo International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar J. Harris; J. Harris International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar R. Verney; R. Verney International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar I. Bondár I. Bondár International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Search for other works by this author on: GSW Google Scholar Author and Article Information D. Di Giacomo International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK D. A. Storchak International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK N. Safronova International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK P. Ozgo International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK J. Harris International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK R. Verney International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK I. Bondár International Seismological Centre, Pipers Lane, Thatcham, Berkshire RG19 4NS, UK Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2014 by the Seismological Society of America Seismological Research Letters (2014) 85 (2): 354–360. https://doi.org/10.1785/0220130143 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. Di Giacomo, D. A. Storchak, N. Safronova, P. Ozgo, J. Harris, R. Verney, I. Bondár; A New ISC Service: The Bibliography of Seismic Events. Seismological Research Letters 2014;; 85 (2): 354–360. doi: https://doi.org/10.1785/0220130143 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 SocietySeismological Research Letters Search Advanced Search The International Seismological Centre (ISC) is a not‐for‐profit organization with the primary mission of producing the definitive summary of the seismicity of the Earth (ISC Bulletin; ISC, 1964–2013). This is achieved thanks to a unique international cooperation in the seismological community that allows the ISC to collect, integrate, and finally process seismological bulletins (location parameters, station data, moment tensor solutions, felt reports, etc.) from approximately 130 agencies worldwide. Seismic (earthquakes or man‐made) events parameters and station data are publicly available via the ISC website (www.isc.ac.uk, last accessed January 2014). In 2012 we started to set up a... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Study on the Effect of Zipingpu Reservoir on the Occurrence of 2008 Wenchuan MS7.9 Earthquake Based on a 3D‐Poroelastic Model

AbstractIt has been well recognized that large reservoir may induce earthquake. After May 12th, 2012 Wenchuan MS7.9 earthquake, people turn to think that it might be triggered by the impoundment of Zipingpu reservoir, which is located a few kilometers away from the epicenter of this devastating event. This scientific issue is still under hot debating to date in both geodynamics and seismology communities. In this paper, we first propose a 3D finite element numerical model of Zipingpu reservoir region based on the poroelastic scenario. Based on the water level fluctuation record of Zipingpu reservoir from the very beginning of impoundment to the occurrence of 2008 Wenchuan earthquake, we calculate the pore pressure and the change of Coulomb stress on the fault plane. Then, we discuss the effects of elastic modulus and diffusivity of fault gouge and materials around the faults. Our primary results indicate that the elastic modulus of fault gouge and the materials around the faults have relatively neglectable effect, compared to that of the diffusive coefficient, on the Coulomb stress change at the hypocenter of this earthquake. The Coulomb stress change at the hypocenter increases coherently with the increasing diffusivity of the faults and their neighboring areas. Given the values of elastic modulus and diffusivity in our model, the change of Coulomb stress at the hypocenter obtained is around 1 kPa when Wenchuan MS7.9 earthquake happened. From the local earthquake catalog after the impoundment of the reservoir, the seismicity activities around Zipingpu reservoir regions does intensified, although the magnitudes of them are almost no more than MS2.2. However, we find that most of the small events happened before Wenchuan MS7.9 earthquake are located in the region of Coulomb stress increases, which indicates that most of the small earthquakes could have direct relationship with the impoundment of Zipingpu reservoir.

Rotaphone, a Self-Calibrated Six-Degree-of-Freedom Seismic Sensor and Its Strong-Motion Records

Rotational seismology is attracting attention in the seismological community including seismic engineers interested in possible damages to man‐made constructions due to strong rotational ground motions. Mathematically, seismic rotation represents the curl of the seismic displacement u , ![Graphic][1] , with Cartesian components: ![Graphic][2] (1) Seismic rotation, due to S waves, is nonzero even in a homogeneous isotropic medium. The inhomogeneity and anisotropy of seismic structures generate more complex wavefield patterns and hence more significant seismic rotations. Moreover, a complex seismic source can contribute considerably to the rotation field, namely in a near‐source zone. In this paper we present a new six‐degree‐of‐freedom (6DOF) seismic sensor called Rotaphone and its strong‐motion records both from an anthropogenic source (blast) and from a tectonic event. By strong rotational motion we mean rotation rate of the order 10−4 rad/s and higher (according to a common convention accepted in the seismological community; see, e.g., Graizer, 2009). The sensor is portable, and easy to install and operate. It has a wide dynamic range of 120 dB; it is able to detect weak ground motions (from the order of 10−7 in SI units) as well as stronger motions (up to the order of 10−1 in SI units). The sensor seems to meet requirements of operative deployment for the needs of strong rotational ground‐motion studies. Rotaphone is a mechanical sensor system for recording ground velocity and determining the rotation rate by measuring the spatial velocity gradients at a point. It is based on differencing records from proximal geophones attached to a rigid frame. The first prototypes based on this principle were presented by Brokesova and Malek (2010) and Brokesova, Malek, and Kolinský (2012). Those instruments measured only the vertical‐axis rotation (torsion) and two perpendicular horizontal velocity components. The 6DOF instrument presented here represents an enhanced design of those … [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif

Surface-wave observations after integrating active and passive source data

Empirical Green's function (EGF) retrieval and turning ambient noise into useful signal by crosscorrelation or seismic interferometry (Curtis et al., 2006) has been a popular topic in recent years in the seismological community. Many have discussed how the interstation distance or its equivalent affects the accuracy of the Green's function that can be retrieved by crosscorrelation of long-range noise between two stations (e.g., Snieder, 2004; Bensen et al., 2007; Halliday and Curtis, 2008; Tsai, 2009; Kimman and Trampert, 2010). It is generally accepted that the necessary or optimum interstation distance strongly depends on source distribution, length of records (and, hence, is naturally related to source distribution), and the duration of the Green's function to be retrieved. Noise generated by a surface source can be efficiently used to reconstruct the Green's function of surface waves if we focus on the accuracy of the phase, and not be too concerned with the amplitude accuracy of the retrieved Green's function (Halliday and Curtis, 2008; Kimman and Trampert, 2010).

Data Products at the IRIS DMC: Stepping Stones for Research and Other Applications

In 2010, the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (DMC) expanded the preexisting effort to generate, archive, and distribute data products derived from the extensive data archives of the center, which include the IRIS Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL), Global Seismographic Network (GSN), EarthScope, and many other data sources. This expansion included dedicating two new full‐time staff to data products and to the development of a new system to manage and distribute them. With community guidance provided by a data products working group (DPWG), DMC has developed a number of freely available unique and increasingly popular data products for the seismological community. In addition, DMC is also archiving and distributing other data products that are produced by community members. A complete list of data products managed by DMC is maintained here: http://www.iris.edu/dms/products. Many of these are available from the Searchable Product Depository (SPUD, http://www.iris.edu/spud), the DMC data product management system. Traditionally, data products result from specialized processing applied during research by the principal investigators and their teams. Products span the range of simple plots or animations derived from waveform data to highly refined models. Some waveform‐processing techniques (e.g., receiver functions) have gained wide community use and can be derived by widely accepted algorithms. Such first‐order data products make ideal candidates for routine generation to provide a standard for the user community. Data products are typically derived from raw data to serve as insightful summaries of the raw time series data, or as quality control metrics, or as foundations or stepping stones to more specialized products and research. The overall goal of the DMC data product effort is to produce and manage a variety of community‐approved and utilized data products that complement the raw data managed at the DMC and ultimately serve …

An Almost Fair Comparison Between Earthworm and SeisComp3

Any earthquake service that maintains a seismic network operates an earthquake monitoring system (EMS), which is a combination of software capable of acquiring, processing, and archiving large volumes of real-time continuous seismic data. Crucially, the processing includes the automatic detection, location, and quantification of earthquakes. Manual review and alert dissemination are typically also core components of an EMS. There are a small number of modern and complete EMSs available to the seismological community; only a couple of these are free. A new seismic network must decide which EMS to operate, and even established networks are periodically required to consider either updating or overhauling their operational EMS. Often, a seismic network has operated a particular EMS for several years and, in some cases, decades. Although there are few options, the selection of the appropriate EMS to operate is not at all a trivial choice. The enduringly popular Earthworm was the first true EMS. Carl Johnson from the U.S. Geological Survey (USGS), a lead developer of the original system, followed a set of design principles that “guide the design and implementation of a seismic processing system”: modularity, system independence, scalability, connectivity, and robustness (from www.earthwormcentral.org/). More than two decades later, these could still serve as the guiding principles for the general design and development of a sustainable EMS. In this opinion piece, we compare two of the leading cost-free options: Earthworm and SeisComP3. This opinion paper is intended to aid network seismologists who need to select or migrate to a new monitoring system for earthquake surveillance. We do not pretend to have the definitive answer to this complex decision. Indeed, selecting the right software is highly network dependent, requiring reflection on the specific network goals, existing network boundary conditions (e.g., field sensors), and available expertise. Nonetheless, we aim to offer a summary …

Recommendation for the discrimination of human-related and natural seismicity

Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology.

FuncLab: A MATLAB Interactive Toolbox for Handling Receiver Function Datasets

Receiver functions have become a widely used tool to study the seismic velocity structure beneath a single station by imaging impedance boundaries where mode conversions from P to S waves occur. In recent years, the community has seen an increase in the amount of broadband seismic data available through systems such as the IRIS Data Management Center (IRIS DMC), requiring new approaches to managing and handling large datasets in computationally efficient ways. Many receiver function studies have focused on tectonic and geodynamic questions on regional scales of a few hundred square kilometers ( e.g. , Zandt et al. 1995; Sheehan et al. 1995; Dueker and Sheehan 1997). These studies typically have utilized data from temporary networks operating on time scales of a few months to a few years. Others have concentrated on global trends, using data from increasing numbers stations that have operated for years or decades ( e.g. , Andrews and Deuss 2008; Lawrence and Shearer 2006; Tauzin et al. 2008). Over the last several years, the seismological community has seen a rapid increase in the number of deployed passive broadband seismic stations and a resulting increase in data available for receiver function analysis. Large initiatives such as EarthScope’s USArray Transportable Array enable immediate open access to data and have provided the community with an order of magnitude more data than in the previous three decades (Figure 1) based on smaller regional temporary studies using data from IRIS PASSCAL-style field experiments ( e.g. , Suckale et al. 2009; Wilson et al. 2005). While the computation of receiver functions has been well studied and is a relatively straightforward and rapid process, an efficient method to analyze and further evaluate very large receiver function datasets is not widely available. In this paper, we present an efficient workflow and …

Expecting the Unexpected: Black Swans and Seismology

Probably no one in the seismological community, or any of the tens of millions of people who would subsequently be affected, was contemplating in detail the possibility of the strong mid-Atlantic region earthquake on the morning of 23 August 2011, during which strong ground motion was experienced by more people than in any other single event in U.S. history. It (inadvisably) emptied buildings in Manhattan and even (briefly) roused the U.S. government from its usual business of partisan siege warfare. Just a few hours before the Virginia earthquake, Colorado experienced one of the largest earthquakes in its history. As I write this, the media is abuzz with coverage of the largest earthquake in Oklahoma history. News from yet another tragic earthquake in Turkey is just now fading from the short-attention-span U.S. media. > 2011 offered a number of examples of novel infrastructural and societal surprises atop the scientific ones... consider the ongoing “Earthquake Trial” in L’Aquila, Italy. Even given the limited state of geological and seismological knowledge of the eastern United States and general intraplate seismicity, the Virginia event was not especially surprising. Indeed things could have been much, much worse ( e.g. , consider the effects of a Charleston 1886-scale event of 6.5 or larger on the eastern seaboard), and the final …

Re-examination of the Potential for Great Earthquakes along the Aleutian Island Arc with Implications for Tsunamis in Hawaii

Hawaii is threatened by tsunamis from circum-Pacific earthquakes and has been hit by major tsunamis from great earthquakes in the prior century in Kamchatka (1952), the Aleutians (1946 and 1957), Chile (1960), and Alaska (1964). Of these, tsunamis generated from great earthquakes along the Alaska-Aleutian Island arc are of particular concern due to their short (4.5–hour) propagation time to Hawaii, which presents the most limited time for coastal evacuation. Historically, the Aleutian earthquakes of 1946 and 1957 produced the largest tele-tsunamis observed in Hawaii (Lander and Lockridge 1989). The 1946 event ( Mw 8.6) killed 159 people with waves reaching up to 16 m height on Molokai. Even though the 1957 event ( Mw 8.6) caused no deaths in Hawaii, a maximum run-up of 16 m was observed on Kauai. Although these two great earthquakes in the Aleutians had substantial tsunami impacts in Hawaii, they are not among the largest seismic events to have occurred globally in the last century. To evaluate the extent of the tsunami threat to Hawaii from the Aleutian Islands, we need to consider the potential for even larger earthquakes in light of the analysis of more than a century of data measuring the Aleutian seismic zone. The motivation for this review is the great Tohoku earthquake of 2011, which occurred in the active seismic region off the coast of East Honshu, Japan, and caused a deadly tsunami in Japan that was felt on shorelines across the Pacific. This magnitude Mw 9.0 event surprised the seismological community with respect to its unexpectedly large magnitude and the size of the generated tsunami ( e.g. , Normile 2011; Monastersky 2011; Showstack 2011). Since the great Sanriku earthquake of 1896 there have been nine damaging earthquakes (magnitude M 7.3 to about 8.6) in the area of the Tohoku earthquake rupture …

Theory of supervirtual refraction interferometry

SUMMARY Inverting for the subsurface velocity distribution by refraction traveltime tomography is a well-accepted imaging method by both the exploration and earthquake seismology communities. A significant drawback, however, is that the recorded traces become noisier with increasing offset from the source position, and so accurate picking of traveltimes in far-offset traces is often prevented. To enhance the signal-to-noise ratio (SNR) of the far-offset traces, we present the theory of supervirtual refraction interferometry where the SNR of far-offset head-wave arrivals can be theoretically increased by a factor proportional to ; here, N is the number of receiver or source positions associated with the recording and generation of the head-wave arrival. There are two steps to this methodology: correlation and summation of the data to generate traces with virtual head-wave arrivals, followed by the convolution of the data with the virtual traces to create traces with supervirtual head-wave arrivals. This method is valid for any medium that generates head-wave arrivals recorded by the geophones. Results with both synthetic traces and field data demonstrate the feasibility of this method. There are at least four significant benefits of supervirtual interferometry: (1) an enhanced SNR of far-offset traces so the first-arrival traveltimes of the noisy far-offset traces can be more reliably picked to extend the useful aperture of the data, (2) the SNR of head waves in a trace that arrive later than the first arrival can be enhanced for accurate traveltime picking and subsequent inversion by later-arrival traveltime tomography, (3) common receiver-pair gathers can be analysed to detect the presence of diving waves in the first arrivals, which can be used to assess the nature of the refracting boundary, and (4) the source statics term is eliminated in the correlation operations so that the timing of the virtual traces is independent of the source excitation time. This suggests the possibility of applying this method to earthquake data recorded by receivers that are inline with the refraction paths and source locations.