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Susan E. Hough

Publications and source records attributed to Susan E. Hough.

At least 73 records · Page 4Linked to original sources
USGS2015

The petroleum geologist and the insurance policy

In a recent study, Hough and Page (2015) presented several lines of evidence suggesting that most of the significant earthquakes in Oklahoma during the twentieth century, including the M w 5.7 El Reno earthquake of 9 April 1952, were likely induced by wastewater injection and possibly secondary oil recovery operations. We undertook an archival search for accounts of this event, which unearthed a newspaper article published immediately following the El Reno earthquake regarding a prominent petroleum geologist in the area who took out a rare earthquake insurance policy less than 60 days before the earthquake struck. In this study we present a historical context for this intriguing coincidence. We present a retrospective of oil industry practices in the early‐ to mid‐twentieth century, gleaned from court records and other industry reports, that potentially bear on the interplay between oil exploration activities and earthquakes, focusing on the Oklahoma City region. We describe events of the day that could plausibly have alerted a geologist to the possibility of induced earthquakes, although there is no indication that the potential for induced earthquakes was widely recognized within the industry at that time.

Oklahoma↗
USGS2015

The 1868 Hayward fault, California, earthquake: Implications for earthquake scaling relations on partially creeping faults

The 21 October 1868 Hayward, California, earthquake is among the best-characterized historical earthquakes in California. In contrast to many other moderate-to-large historical events, the causative fault is clearly established. Published magnitude estimates have been fairly consistent, ranging from 6.8 to 7.2, with 95% confidence limits including values as low as 6.5. The magnitude is of particular importance for assessment of seismic hazard associated with the Hayward fault and, more generally, to develop appropriate magnitude–rupture length scaling relations for partially creeping faults. The recent reevaluation of archival accounts by Boatwright and Bundock (2008), together with the growing volume of well-calibrated intensity data from the U.S. Geological Survey “Did You Feel It?” (DYFI) system, provide an opportunity to revisit and refine the magnitude estimate. In this study, we estimate the magnitude using two different methods that use DYFI data as calibration. Both approaches yield preferred magnitude estimates of 6.3–6.6, assuming an average stress drop. A consideration of data limitations associated with settlement patterns increases the range to 6.3–6.7, with a preferred estimate of 6.5. Although magnitude estimates for historical earthquakes are inevitably uncertain, we conclude that, at a minimum, a lower-magnitude estimate represents a credible alternative interpretation of available data. We further discuss implications of our results for probabilistic seismic-hazard assessment from partially creeping faults.

California↗
USGS2015

Ground motions from the 2015Mw 7.8 Gorkha, Nepal, earthquake constrained by a detailed assessment of macroseismic data

To augment limited instrumental recordings of the M w 7.8 Gorkha, Nepal, earthquake on 25 April 2015 (Nepali calendar: 12 Baisakh 2072, Bikram Samvat), we collected 3831 detailed media and first-person accounts of macroseismic effects that include sufficiently detailed information to assign intensities. The resulting intensity map reveals the distribution of shaking within and outside of Nepal, with the key result that shaking intensities throughout the near-field region only exceeded intensity 8 on the 1998 European Macroseismic Scale (EMS-98) in rare instances. Within the Kathmandu Valley, intensities were generally 6–7 EMS. This surprising (and fortunate) result can be explained by the nature of the mainshock ground motions, which were dominated by energy at periods significantly longer than the resonant periods of vernacular structures throughout the Kathmandu Valley. Outside of the Kathmandu Valley, intensities were also generally lower than 8 EMS, but the earthquake took a heavy toll on a number of remote villages, where many especially vulnerable masonry houses collapsed catastrophically in 7–8 EMS shaking. We further reconsider intensities from the 1833 earthquake sequence and conclude that it occurred on the same fault segment as the Gorkha earthquake.

Gorkha↗
USGS2015

Strong-motion observations of the M 7.8 Gorkha, Nepal, earthquake sequence and development of the N-shake strong-motion network

We present and describe strong-motion data observations from the 2015 M 7.8 Gorkha, Nepal, earthquake sequence collected using existing and new Quake-Catcher Network (QCN) and U.S. Geological Survey NetQuakes sensors located in the Kathmandu Valley. A comparison of QCN data with waveforms recorded by a conventional strong-motion (NetQuakes) instrument validates the QCN data. We present preliminary analysis of spectral accelerations, and peak ground acceleration and velocity for earthquakes up to M 7.3 from the QCN stations, as well as preliminary analysis of the mainshock recording from the NetQuakes station. We show that mainshock peak accelerations were lower than expected and conclude the Kathmandu Valley experienced a pervasively nonlinear response during the mainshock. Phase picks from the QCN and NetQuakes data are also used to improve aftershock locations. This study confirms the utility of QCN instruments to contribute to ground-motion investigations and aftershock response in regions where conventional instrumentation and open-access seismic data are limited. Initial pilot installations of QCN instruments in 2014 are now being expanded to create the Nepal–Shaking Hazard Assessment for Kathmandu and its Environment (N-SHAKE) network.

Seismological Research Letters↗
USGS2015

Introduction to the focus section on the 2015 Gorkha, Nepal, earthquake

It has long been recognized that Nepal faces high earthquake hazard, with the most recent large ( M w >7.5) events in 1833 and 1934. When the 25 April 2015 M w 7.8 Gorkha earthquake struck, it appeared initially to be a realization of worst fears. In spite of its large magnitude and proximity to the densely populated Kathmandu valley, however, the level of damage was lower than anticipated, with most vernacular structures within the valley experiencing little or no structural damage. Outside the valley, catastrophic damage did occur in some villages, associated with the high vulnerability of stone masonry construction and, in many cases, landsliding. The unexpected observations from this expected earthquake provide an urgent impetus to understand the event itself and to better characterize hazard from future large Himalayan earthquakes. Toward this end, articles in this special focus section present and describe available data sets and initial results that better illuminate and interpret the earthquake and its effects.

Gorkha↗
USGS2015

A century of induced earthquakes in Oklahoma?

Seismicity rates have increased sharply since 2009 in the central and eastern United States, with especially high rates of activity in the state of Oklahoma. Growing evidence indicates that many of these events are induced, primarily by injection of wastewater in deep disposal wells. The upsurge in activity has raised two questions: What is the background rate of tectonic earthquakes in Oklahoma? How much has the rate varied throughout historical and early instrumental times? In this article, we show that (1) seismicity rates since 2009 surpass previously observed rates throughout the twentieth century; (2) several lines of evidence suggest that most of the significant earthquakes in Oklahoma during the twentieth century were likely induced by oil production activities, as they exhibit statistically significant temporal and spatial correspondence with disposal wells, and intensity measurements for the 1952 El Reno earthquake and possibly the 1956 Tulsa County earthquake follow the pattern observed in other induced earthquakes; and (3) there is evidence for a low level of tectonic seismicity in southeastern Oklahoma associated with the Ouachita structural belt. The 22 October 1882 Choctaw Nation earthquake, for which we estimate Mw 4.8, occurred in this zone.

Oklahoma↗
USGS2015

The 21 May 2014 M w 5.9 Bay of Bengal earthquake: macroseismic data suggest a high‐stress‐drop event

A modest but noteworthy M w 5.9 earthquake occurred in the Bay of Bengal beneath the central Bengal fan at 21:51 Indian Standard Time (16:21 UTC) on 21 May 2014. Centered over 300 km from the eastern coastline of India (Fig. 1), it caused modest damage by virtue of its location and magnitude. However, shaking was very widely felt in parts of eastern India where earthquakes are uncommon. Media outlets reported as many as four fatalities. Although most deaths were blamed on heart attacks, the death of one woman was attributed by different sources to either a roof collapse or a stampede (see Table S1, available in the electronic supplement to this article). Across the state of Odisha, as many as 250 people were injured (see Table S1), most after jumping from balconies or terraces. Light damage was reported from a number of towns on coastal deltaic sediments, including collapsed walls and damage to pukka and thatched dwellings. Shaking was felt well inland into east‐central India and was perceptible in multistoried buildings as far as Chennai, Delhi, and Jaipur at distances of ≈1600  km (Table 1).

Seismological Research Letters↗
USGS2015

Shaking intensity from injection-induced versus tectonic earthquakes in the central-eastern United States

Although instrumental recordings of earthquakes in the central and eastern United States (CEUS) remain sparse, the U. S. Geological Survey's “Did you feel it?” (DYFI) system now provides excellent characterization of shaking intensities caused by induced and tectonic earthquakes. Seventeen CEUS events are considered between 2013 and 2015. It is shown that for 15 events, observed intensities at epicentral distances greater than ≈ 10 km are lower than expected given a published intensity-prediction equation for the region. Using simple published relations among intensity, magnitude, and stress drop, the results suggest that 15 of the 17 events have low stress drop. For those 15 events, intensities within ≈ 10-km epicentral distance are closer to predicted values, which can be explained as a consequence of relatively shallow source depths. The results suggest that those 15 events, most of which occurred in areas where induced earthquakes have occurred previously, were likely induced. Although moderate injection-induced earthquakes in the central and eastern United States will be felt widely because of low regional attenuation, the damage from shallow earthquakes induced by injection will be more localized to event epicenters than shaking tectonic earthquakes, which tend to be somewhat deeper. Within approximately 10 km of the epicenter, intensities are generally commensurate with predicted levels expected for the event magnitude.

The Leading Edge↗
USGS2014

Shaking from injection-induced earthquakes in the central and eastern United States

In this study I consider the ground motions generated by 11 moderate (M w 4.0-5.6) earthquakes in the central and eastern United States that are thought or suspected to be induced by fluid injection. Using spatially rich intensity data from the USGS “Did You Feel It?” system, I show that the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region, but for all of the events, intensities are lower than values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events. I introduce an effective intensity magnitude, M IE , defined as the magnitude that on average would generate a given intensity distribution. For all 11 events, M IE is lower than the event magnitude by 0.4-1.3 magnitude units, with an average difference of 0.82 units. This suggests that stress drops of injection-induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2-10. However, relatively limited data suggest that intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude, which can be reasonably explained by the shallow focal depth of the events. The results suggest that damage from injection-induced earthquakes will be especially concentrated in the immediate epicentral region.

Bulletin of the Seismological Society of America↗
USGS2014

Earthquake intensity distributions: a new view

Pioneering work by Nicolas Ambraseys and many collaborators demonstrates both the tremendous value of macroseismic data and the perils of its uncritical assessment. In numerous publications he shows that neglect of original sources and/or failure to appreciate the context of historical accounts, as well as use of unreliable indicators such as landslid- ing to determine intensities, commonly leads to inflated magnitude estimates for historical earthquakes. The U.S. Geological Survey “Did You Feel It?” (DYFI) system, which now collects and systematically interprets thousands of first-hand reports from felt earthquakes, provides the opportunity to explore further the biases associated with traditional intensity distributions determined from written (media or archival) accounts. I briefly summarize and further develop the results of Hough (2013), who shows that traditional intensity distrib- utions imply more dramatic damage patterns than are documented by more spatially rich DYFI data, even when intensities are assigned according to the conservative practices estab- lished by Ambraseys’ work. I further consider the separate intensity–attenuation relations that have been developed to characterize intensities for historical and modern earthquakes in California, using traditionally assigned intensities and DYFI intensities, respectively. The results support the conclusion that traditionally assigned intensity values tend to be inflated by a fundamental bias towards reporting of dramatic rather than representative effects. I introduce an empirical correction-factor approach to correct for these biases. This allows the growing wealth of well-calibrated DYFI data to be used as calibration events in the analysis of historical earthquakes

Bulletin of Earthquake Engineering↗
USGS2013

Spatial variability of "Did You Feel It?" intensity data: insights into sampling biases in historical earthquake intensity distributions

Recent parallel development of improved quantitative methods to analyze intensity distributions for historical earthquakes and of web‐based systems for collecting intensity data for modern earthquakes provides an opportunity to reconsider not only important individual historical earthquakes but also the overall characterization of intensity distributions for historical events. The focus of this study is a comparison between intensity distributions of historical earthquakes with those from modern earthquakes for which intensities have been determined by the U.S. Geological Survey “Did You Feel It?” (DYFI) website (see Data and Resources). As an example of a historical earthquake, I focus initially on the 1843 Marked Tree, Arkansas, event. Its magnitude has been previously estimated as 6.0–6.2. I first reevaluate the macroseismic effects of this earthquake, assigning intensities using a traditional approach, and estimate a preferred magnitude of 5.4. Modified Mercalli intensity (MMI) values for the Marked Tree earthquake are higher, on average, than those from the 2011 >Mw 5.8 Mineral, Virginia, earthquake for distances ≤500 km but comparable or lower on average at larger distances, with a smaller overall felt extent. Intensity distributions for other moderate historical earthquakes reveal similar discrepancies; the discrepancy is also even more pronounced using earlier published intensities for the 1843 earthquake. I discuss several hypotheses to explain the discrepancies, including the possibility that intensity values associated with historical earthquakes are commonly inflated due to reporting/sampling biases. A detailed consideration of the DYFI intensity distribution for the Mineral earthquake illustrates how reporting and sampling biases can account for historical earthquake intensity biases as high as two intensity units and for the qualitative difference in intensity distance decays for modern versus historical events. Thus, intensity maps for historical earthquakes tend to imply more widespread damage patterns than are revealed by intensity distributions of modern earthquakes of comparable magnitude. However, intensity accounts of historical earthquakes often include fragmentary accounts suggesting long‐period shaking effects that will likely not be captured fully in historical intensity distributions.

Bulletin of the Seismological Society of America↗
USGS2013

Reverberations on the watery element: A significant tsunamigenic historical earthquake offshore the Carolina coast

We investigate an early nineteenth-century earthquake that has been previously cataloged but not previously investigated in detail or recognized as a significant event. The earthquake struck at approximately 4:30 a.m. LT on 8 January 1817 and was widely felt throughout the southeastern and mid-Atlantic United States. Around 11:00 a.m. the same day, an eyewitness described a 12-inch tide that rose abruptly and agitated boats on the Delaware River near Philadelphia. We show that the timing of this tide is consistent with the predicted travel time for a tsunami generated by an offshore earthquake 6–7 hours earlier. By combining constraints provided by the shaking intensity distribution and the tsunami observation, we conclude that the 1817 earthquake had a magnitude of low- to mid-M 7 and a location 800–1000 km offshore of South Carolina. Our results suggest that poorly understood offshore source zones might represent a previously unrecognized hazard to the southern and mid-Atlantic coast. Both observational and modeling results indicate that potential tsunami hazard within Delaware Bay merits consideration: the simple geometry of the bay appears to catch and focus tsunami waves. Our preferred location for the 1817 earthquake is along a diffuse northeast-trending zone defined by instrumentally recorded and historical earthquakes. The seismotectonic framework for this region remains enigmatic.

South Carolina↗
USGS2013

Crustal structure and fault geometry of the 2010 Haiti earthquake from temporary seismometer deployments

Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Léogâne fault, a north‐dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean‐bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Léogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first‐motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.

Bulletin of the Seismological Society of America↗
USGS2013

Missing great earthquakes

The occurrence of three earthquakes with moment magnitude (Mw) greater than 8.8 and six earthquakes larger than Mw 8.5, since 2004, has raised interest in the long-term global rate of great earthquakes. Past studies have focused on the analysis of earthquakes since 1900, which roughly marks the start of the instrumental era in seismology. Before this time, the catalog is less complete and magnitude estimates are more uncertain. Yet substantial information is available for earthquakes before 1900, and the catalog of historical events is being used increasingly to improve hazard assessment. Here I consider the catalog of historical earthquakes and show that approximately half of all Mw ≥ 8.5 earthquakes are likely missing or underestimated in the 19th century. I further present a reconsideration of the felt effects of the 8 February 1843, Lesser Antilles earthquake, including a first thorough assessment of felt reports from the United States, and show it is an example of a known historical earthquake that was significantly larger than initially estimated. The results suggest that incorporation of best available catalogs of historical earthquakes will likely lead to a significant underestimation of seismic hazard and/or the maximum possible magnitude in many regions, including parts of the Caribbean.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Initial assessment of the intensity distribution of the 2011 M w 5.8 Mineral, Virginia, earthquake

The intensity data collected by the U.S. Geological Survey (USGS) "Did You Feel It?" (DYFI) Website (USGS, DYFI; http://earthquake.usgs.gov/earthquakes/dyfi/events/se/082311a/us/index.html, last accessed Sept 2011) for the M w 5.8 Mineral, Virginia, earthquake, are unprecedented in their spatial richness and geographical extent. More than 133,000 responses were received during the first week following the earthquake. Although intensity data have traditionally been regarded as imprecise and generally suspect (e.g., Hough 2000), there is a growing appreciation for the potential utility of spatially rich, systematically determined DYFI data to address key questions in earthquake ground-motions science (Atkinson and Wald, 2007; Hauksson et al., 2008).

Virginia↗
USGS2012

The crowbar chronicles and other tales

The analysis of historical earthquakes often relies heavily on archival accounts describing the effects of shaking on structures and people. Newspaper articles are among the most common, useful, and easily found sources of information. Dramatic earthquake effects are almost certain to have made the news during historic times; the challenge for modern seismologists is not to be overly swayed by articles that focus on the most dramatic rather than the representative effects in a region. At the other end of the spectrum, rarely does a historical newspaper explicitly note that an earthquake was not felt in a certain area: it is not news when nothing happens. When earthquake effects are subtle, the vexing question is often, did they go unreported entirely?

Seismological Research Letters↗
USGS2012

A terrain-based site characterization map of California with implications for the contiguous United States

We present an approach based on geomorphometry to predict material properties and characterize site conditions using the V S 30 parameter (time‐averaged shear‐wave velocity to a depth of 30 m). Our framework consists of an automated terrain classification scheme based on taxonomic criteria (slope gradient, local convexity, and surface texture) that systematically identifies 16 terrain types from 1‐km spatial resolution (30 arcsec) Shuttle Radar Topography Mission digital elevation models (SRTMDEMs). Using 853 V S 30 values from California, we apply a simulation‐based statistical method to determine the mean V S 30 for each terrain type in California. We then compare the V S 30 values with models based on individual proxies, such as mapped surface geology and topographic slope, and show that our systematic terrain‐based approach consistently performs better than semiempirical estimates based on individual proxies. To further evaluate our model, we apply our California‐based estimates to terrains of the contiguous United States. Comparisons of our estimates with 325 V S 30 measurements outside of California, as well as estimates based on the topographic slope model, indicate our method to be statistically robust and more accurate. Our approach thus provides an objective and robust method for extending estimates of V S 30 for regions where in situ measurements are sparse or not readily available.

California↗