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K. M. Shedlock

Publications and source records attributed to K. M. Shedlock.

12 recordsLinked to original sources
USGS2011

Toward a comprehensive catalog of global historical seismicity

The United States Geological Survey (USGS) and the Colorado School of Mines (CSM) have initiated a project to locate more accurately all earthquakes recorded by instruments during the period 1900 to 1963. Seismicity for this period (hereafter referred to as historical seismicity, following Lee et al . [1988]) is still poorly understood, even for basic parameters such as earthquake locations (see Figure 1). In some cases this is the result of inherent limitations in the distribution, response characteristics, and timing of the instruments. However, locations for most of the pre-1964 earthquakes are poorly determined simply because modern data analysis techniques have yet to be applied to the available arrival-time observations, which are mainly preserved as printed bulletins and not in a computer-ready digital format. The arduous task of hand-entering these data has prevented the systematic analysis and relocation of historical seismicity.

Eos, Transactions, American Geophysical Union↗
USGS2006

Mini-Sosie high-resolution seismic method aids hazards studies

A dramatic example of just how catastrophic earthquake damage can be occurred in 1989, when a nationally televised World Series game in San Francisco was preempted by the M 7.1 Loma Prieta earthquake. The surprising amount and distribution of damage reinforce the importance of seismic-hazard studies in urban areas, where potential for damage and loss of life is greatest. Unfortunately, many large urban centers developed before the advent of seismic-hazard microzonation mapping, ground-response building codes, and standardized air-photo reconnaissance. Decades of building, paving, and utility installation have modified the land surface to the extent that surficial geologic expression of faults and evidence of prehistoric earthquakes are either inaccessible or totally obliterated.

Eos, Transactions, American Geophysical Union↗
USGS2004

Seismic hazard maps of Mexico, the Caribbean, and Central and South America

The growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures due to an insufficient knowledge of existing seismic hazard and/or economic constraints. Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. We have produced a suite of seismic hazard estimates for Mexico, the Caribbean, and Central and South America. One of the preliminary maps in this suite served as the basis for the Caribbean and Central and South America portion of the Global Seismic Hazard Map (GSHM) published in 1999, which depicted peak ground acceleration (pga) with a 10% chance of exceedance in 50 years for rock sites. Herein we present maps depicting pga and 0.2 and 1.0 s spectral accelerations (SA) with 50%, 10%, and 2% chances of exceedance in 50 years for rock sites. The seismicity catalog used in the generation of these maps adds 3 more years of data to those used to calculate the GSH Map. Different attenuation functions (consistent with those used to calculate the U.S. and Canadian maps) were used as well. These nine maps are designed to assist in global risk mitigation by providing a general seismic hazard framework and serving as a resource for any national or regional agency to help focus further detailed studies required for regional/local needs. The largest seismic hazard values in Mexico, the Caribbean, and Central and South America generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes. High hazard values occur in areas where shallow-to-intermediate seismicity occurs frequently. ?? 2004 Elsevier B.V. All rights reserved.

Tectonophysics↗
USGS2001

The Advanced National Seismic System; management and implementation

What is the Advanced National Seismic System? The Advanced National Seismic System (ANSS) is designed to organize, modernize, and standardize operations of seismic networks in the United States to improve the Nation’s ability to respond effectively to damaging earthquakes, volcanoes, and tsunamis. To achieve this, the ANSS will link more than 7,000 national, regional and urban monitoring stations in real time

Fact Sheet↗
USGS1999

Seismic hazard map of the western hemisphere

Vulnerability to natural disasters increases with urbanization and development of associated support systems (reservoirs, power plants, etc.). Catastrophic earthquakes account for 60% of worldwide casualties associated with natural disasters. Economic damage from earthquakes is increasing, even in technologically advanced countries with some level of seismic zonation, as shown by the 1989 Loma Prieta, CA ($6 billion), 1994 Northridge, CA ($ 25 billion), and 1995 Kobe, Japan (> $ 100 billion) earthquakes. The growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures, due to an insufficient knowledge of existing seismic hazard. Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. National, state, and local governments, decision makers, engineers, planners, emergency response organizations, builders, universities, and the general public require seismic hazard estimates for land use planning, improved building design and construction (including adoption of building construction codes), emergency response preparedness plans, economic forecasts, housing and employment decisions, and many more types of risk mitigation. The seismic hazard map of the Americas is the concatenation of various national and regional maps, involving a suite of approaches. The combined maps and documentation provide a useful global seismic hazard framework and serve as a resource for any national or regional agency for further detailed studies applicable to their needs. This seismic hazard map depicts Peak Ground Acceleration (PGA) with a 10% chance of exceedance in 50 years for the western hemisphere. PGA, a short-period ground motion parameter that is proportional to force, is the most commonly mapped ground motion parameter because current building codes that include seismic provisions specify the horizontal force a building should be able to withstand during an earthquake. This seismic hazard map of the Americas depicts the likely level of short-period ground motion from earthquakes in a fifty-year window. Short-period ground motions effect short-period structures (e.g., one-to-two story buildings). The largest seismic hazard values in the western hemisphere generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes. Although the largest earthquakes ever recorded are the 1960 Chile and 1964 Alaska subduction zone earthquakes, the largest seismic hazard (PGA) value in the Americas is in Southern California (U.S.), along the San Andreas fault.

Annals of Geophysics↗
USGS1999

Seismic hazard map of North and Central America and the Caribbean

Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. National, state, and local government, decision makers, engineers, planners, emergency response organizations, builders, universities, and the general public require seismic hazard estimates for land use planning, improved building design and construction (including adoption of building construction codes), emergency response preparedness plans, economic forecasts, housing and employment decisions, and many more types of risk mitigation. The seismic hazard map of North and Central America and the Caribbean is the concatenation of various national and regional maps, involving a suite of approaches. The combined maps and documentation provide a useful regional seismic hazard framework and serve as a resource for any national or regional agency for further detailed studies applicable to their needs. This seismic hazard map depicts Peak Ground Acceleration (PGA) with a 10% chance of exceedance in 50 years. PGA, a short-period ground motion parameter that is proportional to force, is the most commonly mapped ground motion parameter because current building codes that include seismic provisions specify the horizontal force a building should be able to withstand during an earthquake. This seismic hazard map of North and Central America and the Caribbean depicts the likely level of short-period ground motion from earthquakes in a fifty-year window. Short-period ground motions effect short-period structures (e.g., one-to-two story buildings). The highest seismic hazard values in the region generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes.

Annals of Geophysics↗
USGS1998

Near-surface structural model for deformation associated with the February 7, 1812, New Madrid, Missouri, earthquake

The February 7, 1812, New Madrid, Missouri, earthquake (M [moment magnitude] 8) was the third and final large-magnitude event to rock the northern Mississippi Embayment during the winter of 1811–1812. Although ground shaking was so strong that it rang church bells, stopped clocks, buckled pavement, and rocked buildings up and down the eastern seaboard, little coseismic surface deformation exists today in the New Madrid area. The fault(s) that ruptured during this event have remained enigmatic. We have integrated geomorphic data documenting differential surficial deformation (supplemented by historical accounts of surficial deformation and earthquake-induced Mississippi River waterfalls and rapids) with the interpretation of existing and recently acquired seismic reflection data, to develop a tectonic model of the near-surface structures in the New Madrid, Missouri, area. This model consists of two primary components: a north-northwest–trending thrust fault and a series of northeast-trending, strike-slip, tear faults. We conclude that the Reelfoot fault is a thrust fault that is at least 30 km long. We also infer that tear faults in the near surface partitioned the hanging wall into subparallel blocks that have undergone differential displacement during episodes of faulting. The northeast-trending tear faults bound an area documented to have been uplifted at least 0.5 m during the February 7, 1812, earthquake. These faults also appear to bound changes in the surface density of epicenters that are within the modern seismicity, which is occurring in the stepover zone of the left-stepping right-lateral strike-slip fault system of the modern New Madrid seismic zone.

Missouri↗
USGS1990

The effect of S-wave arrival times on the accuracy of hypocenter estimation

Well-constrained hypocenters (latitude, longitude, depth, and origin time) are required for nearly all studies that use earthquake data. We have examined the theoretical basis behind some of the widely accepted “rules of thumb” for obtaining accurate hypocenter estimates that pertain to the use of S phases and illustrate, in a variety of ways, why and when these “rules” are applicable. Results of experiments done for this study show that epicentral estimates (latitude and longitude) are typically far more robust with respect to data inadequacies; therefore, only examples illustrating the relationship between S phase arrival time data and focal depth and origin time estimates are presented. Most methods used to determine earthquake hypocenters are based on iterative, linearized, least-squares algorithms. Standard errors associated with hypocenter parameters are calculated assuming the data errors may be correctly described by a Gaussian distribution. We examine the influence of S-phase arrival time data on such algorithms by using the program HYPOINVERSE with synthetic datasets. Least-squares hypocenter determination algorithms have several shortcomings: solutions may be highly dependent on starting hypocenters, linearization and the assumption that data errors follow a Gaussian distribution may not be appropriate, and depth/origin time trade-offs are not readily apparent. These shortcomings can lead to biased hypocenter estimates and standard errors that do not always represent the true error. To illustrate the constraint provided by S-phase data on hypocenters determined without some of these potential problems, we also show examples of hypocenter estimates derived using a probabilistic approach that does not require linearization. We conclude that a correctly timed S phase recorded within about 1.4 focal depth's distance from the epicenter can be a powerful constraint on focal depth. Furthermore, we demonstrate that even a single incorrectly timed S phase can result in depth estimates and associated measures of uncertainty that are significantly incorrect.

Bulletin of the Seismological Society of America↗