Past Seismicity Research Articles

Assessment of potential tsunamigenic seismic hazard to Sri Lanka

PurposeThe purpose of this paper is to present an assessment of the potential tsunamigenic seismic hazard to Sri Lanka from all active subduction zones in the Indian Ocean Basin.Design/methodology/approachThe assessment was based on previous studies as well as past seismicity of the subducion zones concerned.FindingsAccordingly, four seismic zones capable of generating teletsunamis that could reach Sri Lanka have been identified, namely, Northern Andaman‐Myanmar, Northern Sumatra‐Andaman and Southern Sumatra in the Sunda trench and Makran in the Northern Arabian Sea. Moreover, plausible worst‐case earthquake scenarios and respective fault parameters for each of these seismic zones have been recommended.Research limitations/implicationsHowever, other potential tsunami sources such as seismic activity in the near‐field, submarine landslides and volcanic eruptions have not been considered.Practical implicationsNumerical simulations of tsunami propagation have been carried out for each of the four scenarios in order to assess the potential impact along the coastline of Sri Lanka. Such information relating to the spatial distribution of the likely tsunami amplitudes and arrival times for Sri Lanka would help authorities responsible for evacuation to make a better judgment as to the level of threat in different areas along the coastline, and act accordingly, if a large earthquake were to occur in any of the subduction zones in the Indian Ocean.Originality/valueIn the absence of comprehensive probabilistic assessments of the tsunami hazard to Sri Lanka, this paper's recommendations would provide the necessary framework for the development of deterministic tsunami hazard maps for the shoreline of Sri Lanka.

Present-day stress in the surroundings of 2009 L’Aquila seismic sequence (Italy)

SUMMARY The axial zone of the Apenninic belt in central Italy is a tectonically active region affected by post-orogenic Quaternary extension. The present-day stress field is characterized by a minimum horizontal stress (Shmin) ∼ NE–SW oriented, derived mainly from earthquake focal mechanisms and secondarily from borehole breakouts and fault data. The paper describes the computation of the Shmin orientation along two deep boreholes located in the vicinity of the area hit by the 2009 April 6, Mw 6.3 L’Aquila earthquake. The analysed wells show breakout zones at a depth range between 1.4 and 4.6 km, giving precious information on a depth interval usually not investigated by any other data. The results show an Shmin N81 ± 22° and N74 ± 10° oriented for Varoni 1 and Campotosto 1 wells, respectively. The comparison among the breakouts, the 2009 seismic sequence, the past seismicity and the Quaternary faults indicates a small rotation of Shmin orientation from ∼ NE, in the southern, to ∼ ENE in the northern sector of the study area, where the wells are located. These differences are linked both to the natural variations of data and to the orientation of the main tectonic structures varying from NW–SE in the Abruzzi region to ∼ N–S moving toward the Umbro-Marchean Apennines. The identification of constant Shmin orientations with depth derived from all the examined active stress data, confirms the breakouts as reliable stress indicators also for aseismic areas.

Earthquake Forecasting in Diverse Tectonic Zones of the Globe

We present a simple method for long- and short-term earthquake forecasting (estimating earthquake rate per unit area, time, and magnitude). For illustration we apply the method to the Pacific plate boundary region and the Mediterranean area surrounding Italy and Greece. Our ultimate goal is to develop forecasting and testing methods to validate or falsify common assumptions regarding earthquake potential. Our immediate purpose is to extend the forecasts we made starting in 1999 for the northwest and southwest Pacific to include somewhat smaller earthquakes and then adapt the methods to apply in other areas. The previous forecasts used the CMT earthquake catalog to forecast magnitude 5.8 and larger earthquakes. Like our previous forecasts, the new ones here are based on smoothed maps of past seismicity and assume spatial clustering. Our short-term forecasts also assume temporal clustering. An important adaptation in the new forecasts is to abandon the use of tensor focal mechanisms. This permits use of earthquake catalogs that reliably report many smaller quakes with no such mechanism estimates. The result is that we can forecast earthquakes at higher spatial resolution and down to a magnitude threshold of 4.7. The new forecasts can be tested far more quickly because smaller events are considerably more frequent. Also, our previous method used the focal mechanisms of past earthquakes to estimate the preferred directions of earthquake clustering, however the method made assumptions that generally hold in subduction zones only. The new approach escapes those assumptions. In the northwest Pacific the new method gives estimated earthquake rate density very similar to that of the previous forecast.

Forecasting the Locations of Future Large Earthquakes: An Analysis and Verification

The objective of this paper is to quantify the use of past seismicity to forecast the locations of future large earthquakes and introduce optimization methods for the model parameters. To achieve this the binary forecast approach is used where the surface of the Earth is divided into l° × l° cells. The cumulative Benioff strain of m ≥ m c earthquakes that occurred during the training period, ΔT tr, is used to retrospectively forecast the locations of large target earthquakes with magnitudes ≥m T during the forecast period, ΔT for. The success of a forecast is measured in terms of hit rates (fraction of earthquakes forecast) and false alarm rates (fraction of alarms that do not forecast earthquakes). This binary forecast approach is quantified using a receiver operating characteristic diagram and an error diagram. An optimal forecast can be obtained by taking the maximum value of Pierce’s skill score.

Deterministic Seismic Scenarios for Imphal City

In this article, the spatial variation of ground motion in Imphal City has been estimated by the finite-fault seismological model coupled with site response analysis. The important seismic sources around Imphal City have been identified from the fault map and past seismicity data. The rock level acceleration time histories at Imphal City for the 1869 Cachar (Mw 7.5) earthquake and a hypothetical Mw 8.1 event in the Indo-Burma subduction zone have been estimated by a stochastic finite-fault model. Soil investigation data of 122 boreholes have been collected from several construction projects in Imphal City. Site response analysis has been carried out and the surface level ground motion has been determined for Imphal City for these two earthquake events. The results are presented in the form of peak ground acceleration (PGA) contour map. From the present study it has been ascertained that the maximum amplification for PGA over Imphal City is as high as 2.5. The obtained contour maps can serve as guidelines for identifying vulnerable areas and disaster mitigation in Imphal City.

SASHA: A Computer Program to Assess Seismic Hazard from Intensity Data

Research Article| September 01, 2008 SASHA: A Computer Program to Assess Seismic Hazard from Intensity Data Vera D'Amico; Vera D'Amico Istituto Nazionale di Geofisica e Vulcanologia via della Faggiola, 32 56126 Pisa, Italy damico@pi.ingv.it (V.D.) Search for other works by this author on: GSW Google Scholar Dario Albarello Dario Albarello University of Siena, Department of Earth Sciences via Laterina, 8 53100 Siena, Italy albarello@unisi.it (D.A.) Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2008) 79 (5): 663–671. https://doi.org/10.1785/gssrl.79.5.663 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Vera D'Amico, Dario Albarello; SASHA: A Computer Program to Assess Seismic Hazard from Intensity Data. Seismological Research Letters 2008;; 79 (5): 663–671. doi: https://doi.org/10.1785/gssrl.79.5.663 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 evaluation of seismic hazard over wide territories is a basic tool for planning activities aimed at earthquake damage mitigation. This is commonly performed through probabilistic approaches based on the statistical analysis of past seismicity. Among these, due to its wide application worldwide, the Cornell-McGuire approach (Cornell 1968; McGuire 1978) has become a kind of “standard” methodology for probabilistic seismic hazard assessment (PSHA). In Italy, several national seismic hazard maps were produced in recent years (Slejko et al. 1998; Albarello et al. 2000; MPS Working Group 2004) by following this procedure as implemented... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A Review of Earthquake Statistics: Fault and Seismicity-Based Models, ETAS and BASS

There are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence. The first is fault based. The statistical occurrence of earthquakes is determined for mapped faults. The applicable models are renewal models in that a tectonic loading of faults is included. The second approach is seismicity based. The risk of future earthquakes is based on the past seismicity in the region. These are also known as cluster models. An example of a cluster model is the epidemic type aftershock sequence (ETAS) model. In this paper we discuss an alternative branching aftershock sequence (BASS) model. In the BASS model an initial, or seed, earthquake is specified. The subsequent earthquakes are obtained from statistical distributions of magnitude, time, and location. The magnitude scaling is based on a combination of the Gutenberg-Richter scaling relation and the modified Bath’s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake. Omori’s law specifies the distribution of earthquake times, and a modified form of Omori’s law specifies the distribution of earthquake locations. Unlike the ETAS model, the BASS model is fully self-similar, and is not sensitive to the low magnitude cutoff.

Influence of Time and Space Correlations on Earthquake Magnitude

A crucial point in the debate on the feasibility of earthquake predictions is the dependence of an earthquake magnitude from past seismicity. Indeed, while clustering in time and space is widely accepted, much more questionable is the existence of magnitude correlations. The standard approach generally assumes that magnitudes are independent and therefore in principle unpredictable. Here we show the existence of clustering in magnitude: earthquakes occur with higher probability close in time, space, and magnitude to previous events. More precisely, the next earthquake tends to have a magnitude similar but smaller than the previous one. A dynamical scaling relation between magnitude, time, and space distances reproduces the complex pattern of magnitude, spatial, and temporal correlations observed in experimental seismic catalogs.

Predictability in the ETAS Model of Interacting Triggered Seismicity

As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of seismicity based on interacting events which may trigger a cascade of earthquakes, known as the Epidemic-Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg-Richter law and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large-magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitude M ≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered seismicity models. Quantitatively, the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes.

A Testable Five-Year Forecast of Moderate and Large Earthquakes in Southern California Based on Smoothed Seismicity

We present a five-year forecast of southern California earthquakes with magnitudes 5.0 and greater. The forecast uses earthquake data only, with no explicit use of tectonic, geologic, or geodetic information. The forecast is based on observed regularity of earthquake occurrence rather than on any physical model. The earthquake rate density (probability per unit area, time, and magnitude) is assumed constant in time. We estimate it as the sum of contributions from all magnitude 5 and larger earthquakes in our catalog, which for large quakes extends from 1800 to the present. The contribution from each quake is inversely proportional to epicentral distance and directly dependent on the magnitude. We use the same model to estimate the probable focal mechanisms of future earthquakes, using a weighted sum of the moment tensors of previous quakes. We assume that the rate density is proportional to a smoothed version of past seismicity, using a recently published (Kagan et al. 2006) catalog of California earthquakes. That catalog includes all known earthquakes larger than magnitude 7.5 since 1800 and smaller earthquakes as the lower threshold of completeness has decreased with time. We treat earthquakes as point sources, except that large earthquakes ( M ≥ 6.5) are represented by multiple rectangular dislocation patches (see figure 2 in Kagan et al. 2006). For the forecast that is the subject of this paper, we represent each of the patches by a point source at its center. The estimated rate density depends linearly on the magnitude of past earthquakes and inversely as epicentral distance out to a few hundred kilometers. We assume that 2% of all earthquakes are surprises , assumed uniformly likely in those areas with no earthquakes. Foreshocks and aftershocks are treated as any other earthquake. The method is further described in Kagan and Jackson (1994). We have used the …

Archaeoseismology: Methodological issues and procedure

Archaeoseismic research contributes important data on past earthquakes. A limitation of the usefulness of archaeoseismology is due to the lack of continuous discussion about the methodology. The methodological issues are particularly important because archaeoseismological investigations of past earthquakes make use of a large variety of methods. Typical in situ investigations include: (1) reconstruction of the local archaeological stratigraphy aimed at defining the correct position and chronology of a destruction layer, presumably related to an earthquake; (2) analysis of the deformations potentially due to seismic shaking or secondary earthquake effects, detectable on walls; (3) analysis of the depositional characteristics of the collapsed material; (4) investigations of the local geology and geomorphology to define possible natural cause(s) of the destruction; (5) investigations of the local factors affecting the ground motion amplifications; and (6) estimation of the dynamic excitation, which affected the site under investigation. Subsequently, a ‘territorial’ approach testing evidence of synchronous destruction in a certain region may delineate the extent of the area struck by the earthquake. The most reliable results of an archaeoseismological investigation are obtained by application of modern geoarchaeological practice (archaeological stratigraphy plus geological–geomorphological data), with the addition of a geophysical-engineering quantitative approach and (if available) historical information. This gives a basic dataset necessary to perform quantitative analyses which, in turn, corroborate the archaeoseismic hypothesis. Since archaeoseismological investigations can reveal the possible natural causes of destruction at a site, they contribute to the wider field of environmental archaeology, that seeks to define the history of the relationship between humans and the environment. Finally, through the improvement of the knowledge on the past seismicity, these studies can contribute to the regional estimation of seismic hazard.

Delineation of probable seismic sources in India and neighbourhood by a comprehensive analysis of seismotectonic characteristics of the region

Identification and delineation of seismogenic sources is one of the most important steps in the seismic hazard analysis. This paper presents a comprehensive description of the various tectonic features and the association of seismicity with them to define the probable seismic sources in India and adjacent areas. The plate boundary areas along the Himalayan and the Indo-Burmese arcs, along with the intervening area of northeast India, are characterized by very high level of seismicity. To consider the spatial variation in the seismicity, these areas are divided into several possible seismic sources. In view of the sporadic nature of seismicity in the intraplate area of the peninsular India, it is represented by 21 isolated sources. From a knowledge of the subsurface peninsular features extending up to the Himalaya and the seismicity associated with them, some seismic sources are also delineated transverse to the Himalayan trend in the Indo-Gangetic plains. In all, 81 broad seismic sources are defined by a detailed and critical analysis of the correlation of more than 12,000 past earthquakes with magnitude 4.0 or above with the major tectonic features in the Indian region. Due to the use of an up-to-date database on the past seismicity and a very comprehensive analysis of the seismotectonics of the region, the present study is considered to provide a very realistic basis for evaluation of seismic hazard in India.

Seismic potential of Southern Italy

To improve estimates of the long-term average seismic potential of the slowly straining South Central Mediterranean plate boundary zone, we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs. We express seismic potential (long-term average earthquake recurrence rates as a function of magnitude) in the form of truncated Gutenberg–Richter distributions for seven seismotectonic source zones. Seismic coupling seems to be large or even complete in most zones. An exception is the southern Tyrrhenian thrust zone, where most of the African–European convergence is accommodated. Here aseismic deformation is estimated to range from at least 25% along the western part to almost 100% aseismic slip around the Aeolian Islands. Even so, seismic potential of this zone has previously been significantly underestimated, due to the low levels of recorded past seismicity. By contrast, the series of 19 M6–7 earthquakes that hit Calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration, and seismic potential is revised downward. The southern Tyrrhenian thrust zone and the extensional Calabrian faults, as well as the northeastern Sicilian transtensional zone between them (which includes the Messina Straits, where a destructive M7 event occurred in 1908), all have a similar seismic potential with minimum recurrence times of M ≥ 6.5 of 150–220 years. This potential is lower than that of the Southern Apennines ( M ≥ 6.5 recurring every 60 to 140 years), but higher than that of southeastern Sicily (minimum M ≥ 6.5 recurrence times of 400 years). The high seismicity levels recorded in southeastern Sicily indicate some clustering and are most compatible with a tectonic scenario where the Ionian deforms internally, and motions at the Calabrian Trench are small. The estimated seismic potential for the Calabrian Trench and Central and Western Sicily are the lowest (minimum M ≥ 6.5 recurrence times of 550–800 years). Most zones are probably capable of generating earthquakes up to magnitudes 7–7.5, with the exception of Central and Western Sicily where maximum events sizes most likely do not exceed 7.

LONG-TERM RATES OF FAULTING DERIVED FROM COSMOGENIC NUCLIDES AND SHORT-TERM VARIATIONS CAUSED BY GLACIAL-INTERGLACIAL VOLUME CHANGES OF GLACIERS AND LAKES

Seismic hazard evaluations on major faults in Earth's crust are based on their slip histories, which reflect the frequency of earthquakes that ruptured a fault in the past. On a 100 000-year timescale, the slip rate of a fault can be determined by dating geomorphic surfaces that are offset by a fault. Application of this method to alluvial fan surfaces and river terraces offset by thrust faults in Tibet yields long-term slip rates of less than 1mm/a. Slip rates on a 10 000-year timescale are derived from paleoseismologic data and document that faults experience considerable slip rate variations on timescales of 100 to 1000 years. In particular, slip rates are often considerable higher in the present interglacial, the Holocene, than during the last glacial period, the Late Pleistocene. The causes of this behavior have remained enigmatic but their assessment is essential for an accurate evaluation of a fault's past and future seismicity. Numerical experiments show that the retreat of lakes and glaciers at the end of the last glacial period can cause an increase in the Holocene slip rate of a fault. Such a correlation between enhanced seismicity and climate-driven mass fluctuations on Earth's surface is best documented for the Wasatch Fault, Utah.

Earthquake statistics at Parkfield: 2. Probabilistic forecasting and testing

In paper 1 (Schorlemmer et al., 2004) we showed that the spatial b value (of the Gutenberg‐Richter relation) distribution at the Parkfield segment of the San Andreas fault remained stationary for the past 35 years. In this paper (paper 2) we extend those results, construct two probabilistic forecasts (H1 with a spatially varying b value and H2 with a uniform b value), and test these hypotheses against each other. Both hypotheses use a spatially varying seismicity level (a value) determined from past seismicity. We used a range of sampling parameters (magnitude threshold, cell size, etc.) to assure robust results. We found that in most of the tests, hypothesis H1 showed a higher likelihood than H2, although both are a poor approximation to the seismicity data. The most positive results for H1 are obtained for testing magnitude ranges down to M = 1.5 and with sampling radii as defined in paper 1 as appropriate for Parkfield. The superior performance of H1 suggests that spatially varying b values should be considered in earthquake forecasts.

Remotely Triggered Seismicity in the Yellowstone National Park Region by the 2002 Mw 7.9 Denali Fault Earthquake, Alaska

Coincident with the arrival of low-frequency, large-amplitude surface waves of the Mw 7.9 Denali fault earthquake (DFE), an abrupt increase in seismicity was observed in the Yellowstone National Park region, despite the large epicentral distance of 3100 km. Within the first 24 hr following the DFE mainshock, we located more than 250 earthquakes, which occurred throughout the entire Yellowstone Na- tional Park region. The elevated seismicity rate continued for about 30 days and followed a modified Omori law decay with a P value of 1.02 ! 0.07. For a declus- tered earthquake catalog, the seismicity following the 2002 DFE uniquely stands out with a significance of 30r. The increase in seismicity occurred over all magnitude bands. In general, we observed that seismicity following the DFE outlined the spatial pattern of past seismicity routinely observed in the Yellowstone National Parkregion. However, we found significant differences in triggered seismicity inside and outside the caldera. Earthquakes inside the Yellowstone caldera occurred preferentially as clusters close to major hydrothermal systems, were of larger magnitude, and seis- micity decayed more rapidly. This suggests that either different trigger mechanisms were operating inside and outside the caldera or that the crust responded differently to the same trigger mechanism depending on its different mechanicalstate.Compared with other sites that experienced remote earthquake triggering following the 2002 DFE, Yellowstone showed the most vigorous earthquake activity. We attribute this to strong directivity effects of the DFE, which caused relatively large peak dynamic stresses (0.16-0.22 MPa) in Yellowstone, and to the volcanic nature of Yellowstone.

Estimation of the Maximum Earthquake Magnitude, m max

This paper provides a generic equation for the evaluation of the maximum earthquake magnitude m max for a given seismogenic zone or entire region. The equation is capable of generating solutions in different forms, depending on the assumptions of the statistical distribution model and/or the available information regarding past seismicity. It includes the cases (i) when earthquake magnitudes are distributed according to the doubly-truncated Gutenberg-Richter relation, (ii) when the empirical magnitude distribution deviates moderately from the Gutenberg-Richter relation, and (iii) when no specific type of magnitude distribution is assumed. Both synthetic, Monte-Carlo simulated seismic event catalogues, and actual data from Southern California, are used to demonstrate the procedures given for the evaluation of m max. The three estimates of m max for Southern California, obtained by the three procedures mentioned above, are respectively: 8.32 ± 0.43, 8.31 ± 0.42 and 8.34 ± 0.45. All three estimates are nearly identical, although higher than the value 7.99 obtained by Field et al. (1999). In general, since the third procedure is non-parametric and does not require specification of the functional form of the magnitude distribution, its estimate of the maximum earthquake magnitude m max is considered more reliable than the other two which are based on the Gutenberg-Richter relation.

Estimation of Site Effects in Beijing City

For the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media, the database of 3-D geophysical structures for Beijing City has been built up to model the seismic ground motion in the City, caused by the 1976 Tangshan and the 1998 Zhangbei earthquakes. The hybrid method, which combines the modal summation and the finite-difference algorithms, is used in the simulation. The modeling of the seismic ground motion, for both the Tangshan and the Zhangbei earthquakes, shows that the thick Quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the City. Therefore the thickness of the Quaternary sediments in Beijing City is the key factor controling the local ground effects. Four zones are defined on the base of the different thickness of the Quaternary sediments. The response spectra for each zone are computed, indicating that peak spectral values as high as 0.1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 Sanhe-Pinggu occurs.

Changes in geyser eruption behavior and remotely triggered seismicity in Yellowstone National Park produced by the 2002 M 7.9 Denali fault earthquake, Alaska

Research Article| June 01, 2004 Changes in geyser eruption behavior and remotely triggered seismicity in Yellowstone National Park produced by the 2002 M 7.9 Denali fault earthquake, Alaska S. Husen; S. Husen 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA Search for other works by this author on: GSW Google Scholar R. Taylor; R. Taylor 2National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming 82190, USA Search for other works by this author on: GSW Google Scholar R.B. Smith; R.B. Smith 3Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA Search for other works by this author on: GSW Google Scholar H. Healser H. Healser 4National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming 82190, USA Search for other works by this author on: GSW Google Scholar Author and Article Information S. Husen 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA R. Taylor 2National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming 82190, USA R.B. Smith 3Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA H. Healser 4National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming 82190, USA Publisher: Geological Society of America Received: 03 Dec 2003 Revision Received: 05 Feb 2004 Accepted: 17 Feb 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (6): 537–540. https://doi.org/10.1130/G20381.1 Article history Received: 03 Dec 2003 Revision Received: 05 Feb 2004 Accepted: 17 Feb 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S. Husen, R. Taylor, R.B. Smith, H. Healser; Changes in geyser eruption behavior and remotely triggered seismicity in Yellowstone National Park produced by the 2002 M 7.9 Denali fault earthquake, Alaska. Geology 2004;; 32 (6): 537–540. doi: https://doi.org/10.1130/G20381.1 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 SocietyGeology Search Advanced Search Abstract Following the 2002 M 7.9 Denali fault earthquake, clear changes in geyser activity and a series of local earthquake swarms were observed in the Yellowstone National Park area, despite the large distance of 3100 km from the epicenter. Several geysers altered their eruption frequency within hours after the arrival of large-amplitude surface waves from the Denali fault earthquake. In addition, earthquake swarms occurred close to major geyser basins. These swarms were unusual compared to past seismicity in that they occurred simultaneously at different geyser basins. We interpret these observations as being induced by dynamic stresses associated with the arrival of large-amplitude surface waves. We suggest that in a hydrothermal system dynamic stresses can locally alter permeability by unclogging existing fractures, thereby changing geyser activity. Furthermore, we suggest that earthquakes were triggered by the redistribution of hydrothermal fluids and locally increased pore pressures. Although changes in geyser activity and earthquake triggering have been documented elsewhere, here we present evidence for changes in a hydrothermal system induced by a large-magnitude event at a great distance, and evidence for the important role hydrothermal systems play in remotely triggering seismicity. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Predictability in the Epidemic‐Type Aftershock Sequence model of interacting triggered seismicity

As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of seismicity on the basis of interacting events which may trigger a cascade of earthquakes, known as the Epidemic‐Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg‐Richter law, and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large‐magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitude M ≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered seismicity models. Quantitatively, the fundamental limits of predictability found here are only lower bounds of the true values corresponding to the full information on the spatial location of earthquakes.