Natural HazardsNatural Hazards johncallahan Fri, 06/25/2010 - 09:38
Natural Hazards in DelawareNatural Hazards in Delaware johncallahan Mon, 07/13/2009 - 14:19
Natural hazards are those events in the physical environment that present risks to human life or property. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising emergency management agencies on natural hazards, and are included in the Delaware Emergency Operations Plan as an agency having a vital role in dealing with floods, northeaster/extratropical storms, droughts, earthquakes, sinkholes, and dam failures.
Because of the risk of coastal flooding in southern Delaware, the DGS conducts a program to document the effect of tides and winds on coastal erosion, especially for events with potentially large human impact. One effort as part of this program was a study of historical accounts of the effects of a Category 1 hurricane that swept northward from the Outer Banks of North Carolina, hitting Delaware on October 23, 1878. A storm surge in Delaware Bay raised water levels 6 feet in one hour in some areas, and the highest water levels in the Delaware River at Wilmington were as much as 12 feet above present sea level. More than 100 fatalities were attributed to the hurricane and property damage may have been as much as $150 million in todayâs currency. This storm may well be the hurricane of record for the Delaware region and provides a worst-case scenario for a modern hurricane.
Northeasters are a natural hazard that affects Delaware. Northeasters are storms with galeforce or stronger winds from the northeast generated by low-pressure systems offshore the U.S. eastern seaboard. These generate storm waves that can result in significant beach erosion. The duration of the storm is considered a critical factor in the severity of the erosion. Two severe northeasters between January 26 and February 6, 1998 brought tropical storm-force wind gusts to the Delaware coast. They produced the third and fourth highest tides measured at Breakwater Harbor near Lewes, high tides of record at the Coast Guard Station at Indian River Inlet and along Indian River at Rosedale Beach, and 20-ft-high waves at a buoy offshore the Delaware-Maryland state line, which caused some overwash of coastal dunes and localized coastal flooding. Few structures were damaged. In contrast, the severity of these storms is dwarfed by the devastating northeaster of March, 1962. Overwash was pervasive along the entire length of the coast; few sand dunes were left intact and barrier islands were essentially flattened. Most structures adjacent to the beach were damaged. However, tides were comparable for these storms; the 1962 storm had five successive high tides that were well above normal, yet the February 1998 storm had several high tides at similar levels as well as low tides that were higher than those of the 1962 storm. The difference in destruction at similar tide levels suggests that wave conditions may have been more severe in the 1962 storm. Given the extensive development of the coastline since 1962, a storm of similar magnitude would today likely cause damage in the billions of dollars and potentially result in human casualties.
Assessment of storm event risks and response strategies depends, in part, on a sound understanding of hydrology and geology. The coastal regions of southern Delaware are impacted by coastal erosion and flooding during large storms, and the Piedmont of northern Delaware is susceptible to flash flooding during major rain events. The DGS serves on the Delaware Emergency Management Agencyâs (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and usually have staff located at the Delaware Emergency Operations Center during storm emergencies. We have recently been involved in the development of the Delaware Environmental Observation System in cooperation with DEMA and the Office of the State Climatologist. As part of this, a Coastal Flood Risk Analysis System has been proposed that will integrate stream-flow and tide-gage data with meteorological information in a network to be used for real-time flood analysis/prediction and emergency planning, response, and recovery operations. Other natural disaster-related activities include the DEMA Northeaster Task Force, the DEMA Technical Assessment Center for Natural Disasters, the DEMA State Hazard Mitigation Team, and advising on development of a statewide Dam Safety Program.
Earthquakes are a natural hazard that occur in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677, and 69 earthquakes have been documented or suspected in Delaware since 1871. Although Delaware does not face the same degree of earthquake hazard as other, more seismically active parts of the county, FEMA and the USGS in 1997 reclassified Delaware from a low seismic risk to a moderate seismic risk. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). In the memory of many Delawareans is the 1973 earthquake, which was a magnitude 3.8 temblor (Modified Mercalli VVI).
Another hazard studied by the DGS is sinkholes. Geologic mapping in the Hockessin area shows an area underlain by marble and other carbonate bearing rocks that are particularly susceptible to sinkhole formation. At the request of the New Castle County government, DGS staff regularly review consultantsâ reports related to proposed construction activities in carbonate areas. We also have visited and educated concerned citizens when sinkholes have appeared on their property. Our input helps guide the development of relevant ordinances related to land-use planning and construction activities in these areas.
EarthquakesEarthquakes johncallahan Fri, 06/25/2010 - 09:45
Overview of Earthquakes in DelawareOverview of Earthquakes in Delaware johncallahan Sat, 06/27/2009 - 00:10
Every year approximately 3,000,000 earthquakes occur worldwide. Ninety eight percent of them are less than a magnitude 3. Fewer than 20 earthquakes occur each year, on average, that are considered major (magnitude 7.0 - 7.9) or greater (magnitude 8 and greater). Between 2000 and 2009, the United States experienced approximately 32,000 earthquakes; six were considered major and occurred in either Alaska or California.
USGS Earthquake Lists, Maps, and Statistics: https://earthquake.usgs.gov/earthquakes/browse/.
Earthquakes do not occur exclusively in the western United States. Seven events with magnitudes greater than 6.0 have occurred in the central and eastern sections of the United States since 1811. Of these, four occurred near New Madrid, Missouri between 1811 and 1812, and one occurred in Charleston, South Carolina, in 1886. The largest event in Delaware occurred in 1871 and had an estimated magnitude 4.1. The largest recorded event in Delaware occurred in 1973 and had an estimated magnitude of 3.8.
In 1997, Delaware was reclassified from being a low seismic risk state to being a medium seismic risk state by the U.S. Geological Survey (USGS) and the Federal Emergency Management Agency (FEMA).
The Delaware Geological Survey currently operates seismic stations in Delaware. Fifty-eight earthquakes have been documented in Delaware since 1871. Refer to Baxter (2000) and http://www.dgs.udel.edu/delaware-geology/catalog-delaware-earthquakes-s… for more details about the DGS Seismic Network, Delaware Earthquake Catalog, and for documentation of earthquakes.
An earthquake occurred in Delaware on October 9, 1871, and caused severe property damage. In Wilmington, Delaware's largest city, chimneys toppled, windows broke, and residents were quite bewildered by the unusual event. Lighter damage was sustained in northern Delaware at Newport, New Castle, and in Oxford, Pennsylvania. Earth noises, variously described as "rumbling" and "explosive," accompanied the shock in several areas.
A tremor in March 1879 beneath the Delaware River, not far from Dover, was felt "strongly" in that area according to old seismic records. The records, however, do not describe the "strong" effects.
On May 8, 1906, a shock occurred in Delaware just three weeks after the noted San Francisco earthquake in California. Records state this shock was strong at Seaford, in southwest Delaware, but list no details concerning the event.
Two tremors, both below intensity V, occurred in Delaware, one on the Lower Delaware in December 1937, and one near Wilmington in January 1944.
Parts modified from Earthquake Information Bulletin, May - June 1971, Volume 3, Number 3.
- Catalog of past earthquakes in Delaware
- Special Publication 23: Earthquake Basics
- Map of past earthquakes in Delaware
- USGS Real-time map of M1+ earthquakes recorded
- USGS Earthquake Hazards Program
- Seismic Hazard Map of Delaware (USGS)
- RI39 Earthquakes in Delaware and Nearby Areas, June 1973 - June 1984
More information about the frequency, locations, and science of earthquakes can be found in the adjacent pages on this site and in the DGS report: Special Publication 23: Earthquake Basics.
Catalog of Delaware Earthquakes SpreadsheetCatalog of Delaware Earthquakes Spreadsheet rockman Fri, 07/31/2009 - 15:11
The occurrences of earthquakes in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey are well documented by both historical and instrumental records. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677. One of the earliest known events occurred in 1737 and was felt in Philadelphia and surrounding areas. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). The second largest event occurred in the Delaware area in 1973 (magnitude 3.8 and maximum Modified Mercalli Intensity of V-VI). The epicenter for this event was placed in or near the Delaware River. Sixty-nine earthquakes have been documented or suspected in Delaware since 1871.
The Delaware earthquake data is listed below in table format, can be downloaded in Excel and ESRI shapefile format, and is also displayed as a Google Map at http://www.dgs.udel.edu/delaware-geology/delaware-earthquake-map.
Earthquake Felt ReportEarthquake Felt Report johncallahan Thu, 07/30/2009 - 10:39
Did you feel an earthquake? If so, please complete our Earthquake Felt Report below. Please answer every question to the best of your ability. Either fill in the blanks where called for or check the response that best describes the event. If a particular question does not apply or if you don't know how to respond, simply skip it and go on to the next. You can review and modify answers to all the questions at any time. Feel free to include any additional information in the Additional Comments box at the end of this form.
Delaware Earthquake MapDelaware Earthquake Map johncallahan Thu, 11/30/2017 - 17:33
Earthquake data mapped below was taken from the Catalog of Delaware Earthquakes.
More details and information on earthquakes in Delaware can be found in the following:
The Earthquake of August 23, 2011The Earthquake of August 23, 2011 johncallahan Tue, 08/23/2011 - 22:58
Delaware and surrounding areas experienced an earthquake event on the afternoon of Tuesday, August 23, 2011. According to the US Geological Survey, a magnitude 5.8 earthquake struck at 1:51 p.m. in central Virginia, in an area referred to as "the Central Virginia Seismic Zone" because of its relatively active earthquake activity for the region. The epicenter was located five miles south-southwest of Mineral, Virginia, with the quake was focused at a depth of 6 km (3.7 miles) below the surface. The Virginia Geological Survey reports that this is the largest Virginia earthquake known in historic times. A few small aftershocks have occurred in the hours afterward.
How was this earthquake felt in Delaware?
In Delaware, the earthquake was felt in many locations from northernmost New Castle County to coastal and inland Sussex County. The Delaware Geological Survey website had "felt reports" completed by more than 300 respondents as of 5:00 pm on Aug 23 and over 500 respondents by the evening of Aug 24 (thank you to all of you who replied!). Preliminarily, these responses indicate a Mercalli Intensity of III to IV. The average intensity of building shaking reported by respondents was "moderate." The majority of respondents noted movement or shaking of furniture such as, bookcases, chairs, and computer equipment, some window shaking, and a few overturned items such as picture frames, bottles, and sculptures.
As of 4:00 pm, the US Geological Survey website had received reports from 108 individuals in Delaware with an average intensity reply of 3.3, so between Mercalli III and IV. In the area of central Virginia near the earthquake epicenter, intensities of VII or "Very Strong" were reported, a level strong enough to make standing difficult and to damage poorly built structures. The USGS also received numerous responses from throughout the eastern United States.
How is the strength of an earthquake measured?
The intensity can be gauged using the Mercalli intensity scale, which is characterized by how a quake feels to the observer. A Mercalli intensity of III is considered "Slight." It is felt by people indoors, especially on the upper floors of buildings. A Mercalli intensity of IV is termed "Moderate". It is felt indoors and, by some people, outdoors. Dishes and windows are commonly disturbed and rattle; it may give the sensation of a heavy truck striking a building. These two categories fit most of our reports from Delaware.
The Richter scale measures the energy released by an earthquake. Geophysical sensors called seismometers measure the amount of shaking of the ground at numerous locations; in Delaware, we have five seismic stations that cover all three counties. The August 23 temblor fell in the upper end of the Moderate strength range, between Richter magnitudes 5.0 and 5.9. An interesting fact to remember about the Richter scale â an increase of one number, such as from 5 to 6, means a 10-time increase in the amplitude of shaking and 33-time increase in energy released. This 5.9 event had considerably more energy than the magnitude 3.8 quake that occurred in Delaware in 1973.
Why did this earthquake occur?
The Virginia Geological Survey notes that the earthquake activity in the area is associated with old faults related to movements of the earthâs tectonic plates related to ancient mountain building episodes that were followed by the opening of the Atlantic Ocean about 150 million years ago. The opening of the Atlantic Ocean was accompanied by cracking of the earth's crust, or faulting, along eastern North America. Since the period of this rifting ended, the east coast has been fairly quiet tectonically, in contrast with the tectonically active western coast of the United States. Nevertheless, there are areas that still experience a gradual accumulation of tectonic stress that is occasionally released in the form of an earthquake.
Why did we feel this earthquake in Delaware so far from its central Virginia source?
The geology of the Middle Atlantic region of the east coast favors the travel of earthquake energy for great distances. The earthquake epicenter was located in the Virginia Piedmont, an area underlain by hard basement rocks that predate the opening of the present-day Atlantic Ocean. To the west lie ancient hard rocks of the Appalachian Mountains. To the east, the hard basement rocks are overlain by a blanket of softer sediments that thickens toward the Atlantic Ocean. The hard basement rocks of our region have been in generally the same configuration, with gradual sinking, for the last 150 million years. Earthquake energy can travel well through these hard, cold ancient rocks, in contrast with areas such as California where there is abundant faulting and softer rocks, which absorb the energy more quickly.
The DGS will update this page with additional information, as it becomes available, on the earthquake of August 23, 2011.
The Earthquake of November 30, 2017The Earthquake of November 30, 2017 johncallahan Mon, 12/18/2017 - 09:36
The largest measured earthquake to occur within Delaware was recorded on November 30, 2017. The magnitude 4.1 temblor occurred at 4:47 p.m. with an epicenter located 6 miles northeast of Dover in Bombay Hook National Wildlife Refuge, according to data reported by the U.S. Geological Survey. Analysis of the shaking associated with the Dover earthquake indicates that the source was approximately 5 miles (around 26,000 ft) beneath the land surface in deep crystalline basement rocks and had a predominantly strike-slip direction of motion (side-ways movement along a fault zone), probably along a deep pre-existing fault related to the past tectonic episodes.
How did Delaware Geological Survey scientists confirm that an earthquake had occurred?
DGS operates a network of seismic stations in the state of Delaware to monitor earthquakes and feeds data into the Lamont Doherty Seismographic Network as well as the U.S. Geological Survey. These stations provide publically available, real-time data on seismic signals (or wave energy generated by earthquakes) that occur. The DGS seismic station located in Greenville in New Castle County was the first station to receive the seismic wave from this earthquake.
How was this earthquake felt in Delaware and surrounding areas?
The Dover earthquake of 2017 was felt in locations throughout the state of Delaware and along the eastern seaboard from central Virginia to Massachusetts. Reports compiled on the internet by the USGS and DGS indicate a Modified Mercalli Intensity of IV felt closest to the epicenter and III around most of the region. An intensity of IV is generally associated with light shaking that is felt by many indoors but not as commonly felt outdoors. Dishes, windows, and doors may be disturbed; walls make cracking sound; and the earthquake may have a sensation like heavy truck striking building. An intensity of III is commonly quite noticeable to persons indoors, especially on upper floors of buildings, but in many people may not recognize it as an earthquake. It may feel similar to vibrations from the passing of a truck.
As of Dec 15, 2017, the Delaware Geological Survey website had received approximately 260 "felt reports" from individuals in and around Delaware, with an average intensity reply of 3.X, so between Mercalli III and IV. Higher intensities, commonly VI, were reported closer to the epicenter, mostly in Kent County, many of the reports associated with shaking of dishes, teapots, and lamps. The USGS also has received nearly 17,000 reports through the internet from throughout the northeastern United States.
How is the strength of an earthquake measured?
The strength of an earthquake can be estimated by how it feels to people in the area or measured using seismic equipment. The Mercalli intensity scale is characterized by how a quake feels to the observer. A Mercalli intensity of III is considered “Weak” or "Slight." It is felt by people indoors, especially on the upper floors of buildings. A Mercalli intensity of IV is termed “Light” to "Moderate". It is felt indoors and, by some people, outdoors. Dishes and windows are commonly disturbed and rattle; it may give the sensation of a heavy truck striking a building.
The Richter scale measures the energy released by an earthquake and is determined using seismic equipment. Geophysical sensors called seismometers measure the amount of shaking of the ground at numerous locations; in Delaware, we have five seismic stations that cover all three counties. The Dover M4.1 temblor fell in the lower end of the “Light” strength range, the class that includes Richter magnitudes 4.0 and 4.9. An interesting fact to remember about the Richter scale is that an increase of one number, such as from 4 to 5, means a 10-time increase in the amplitude of shaking and 33-time increase in energy released. This exponential increase in energy is why the 5.8 event in August 2011was felt more strongly by most Delawareans than this magnitude 4.1 quake near Dover; a magnitude 5.8 earthquake represents more than 350 times the energy of a magnitude 4.1 quake.
Why did this earthquake occur?
The geology of the Dover area is characterized by soft sediments and sedimentary rocks near the earth’s surface and hard basement rocks below approximately 4000 ft depth. The hard basement rocks are thought to be similar to the rocks exposed at the land surface in the hilly Appalachian Piedmont region of northern Delaware. Those basement rocks are thought to contain old faults formed by tectonic movements of the earth’s crustal plates. The tectonic episodes that formed eastern North America include a series of continental collisions that built the Appalachian Mountains in several phases between 440 and 280 millions of years ago. This was followed, between around 230 and 190 million years ago, by the separation of North American tectonic plate from an adjacent plate, creating rift faults along the edges and beginning the opening of the Atlantic Ocean. Since this rifting ended around 190 million years ago, the east coast has been fairly quiet tectonically. Ancient faults related to these tectonic episodes exist beneath us and are mostly quiet but in some area can experience a gradual accumulation of tectonic stress that is occasionally released in the form of an earthquake. However, in contrast with the tectonically active western coast of the United States, Delaware does not have a major fault line, like the well-known San Andreas fault system in California. Instead, Delaware is situated away from the edge of the North American Continental Plate, which is located a few thousand miles from Delaware in the Atlantic Ocean, placing the region at less risk for earthquake.
Why was this earthquake felt beyond Delaware?
The geology of the Middle Atlantic region of the east coast favors the travel of earthquake energy for great distances. The earthquake source was centered near Dover, approximately 25,000 beneath the Delaware Coastal Plain, deep in hard, ancient basement rocks of the North American continental crust. The basement rocks are overlain by a blanket of softer sediments that progressively thins toward the Piedmont region in northern Delaware, to where the basement rocks are exposed at the surface,and are exposed as the hard rocks we see in the Piedmont province of the Appalachian Mountains, a trend that extends along the east side of the Appalachian Mountains, including the Baltimore area, northernmost Delaware, and the Philadelphia area. Earthquake energy can travel well through the hard, cold ancient rocks that underlie our region, in contrast with areas such as California where there is abundant faulting and softer rocks that absorb the energy more quickly.
The ability of the Piedmont rocks to efficiently transfer earthquake energy is likely responsible for the northeast-trending line of “felt reports” that extend from northern Virginia to New England, and roughly follows the trend of the Piedmont. The hard basement rocks of our region have been in generally the same configuration, with gradual sinking, for the last 180 million years.
How often do earthquakes occur in Delaware?
The earthquake on Nov 30, 2017 was the fifty-eighth documented event in Delaware since 1871, but it is only about every decade or so that there is an earthquake that people would feel. To put that into perspective, approximately 3 million earthquakes occur worldwide each year, but ninety eight percent of them are less than a magnitude 3.
The 2017 Dover earthquake matched the previous largest event in Delaware, which occurred in 1871 and was estimated to have had a magnitude 4.1 based on the historical accounts of shaking. The largest previously recorded (by instrumentation) event in Delaware occurred in 1973 and had an estimated magnitude of 3.8.
Real-time Earthquake MapsReal-time Earthquake Maps johncallahan Mon, 02/15/2010 - 11:02
- https://earthquake.usgs.gov/earthquakes/map/ (USGS, by default, the above map will show M2.5 earthquakes that occurred in the past 1 day.)
- https://earthquaketrack.com/p/united-states/delaware/recent (Earthquake Track, this map shows recent earthquakes M1.5 or greater.)
- http://ds.iris.edu/seismon/? (IRIS Seismic Monitor)
- http://seismo.berkeley.edu/seismo.real.time.map.html (Berkeley Seismology Lab)
More resources on current earthquake monitoring
Investigating the Causes of Earthquakes in DelawareInvestigating the Causes of Earthquakes in Delaware johncallahan Fri, 07/31/2009 - 00:09
DGS Seismic NetworkDGS Seismic Network johncallahan Fri, 06/25/2010 - 09:52
Seismic Network MapSeismic Network Map johncallahan Thu, 07/30/2009 - 11:10
The DGS maintains its own network of seismometers to detect local earthquake activity. Following an earthquake swarm in 1972, the DGS established its first seismometer station in Newark. The network now consists of five seismic stations spread across the state: three stations in the Newark-Wilmington area, one at the DEMA office in southern New Castle County, and one at the Sussex County Emergency Operations Center. Signals are recorded on paper and captured digitally using Earthworm, a seismic processing system developed by the USGS. These records are shared nationally through participation in the Advanced National Seismic System Network, the Lamont-Doherty Cooperative Seismographic Network, the Northeast U.S. Seismic Network, and the Southeast U.S. Seismic Network. Small local earthquakes and larger earthquakes from other parts of the country and the world are clearly resolved by the network.
Bellevue State Park (BVD) Seismic StationBellevue State Park (BVD) Seismic Station johncallahan Tue, 07/28/2009 - 00:49
The seismometer located at Bellevue State Park is placed on the Brandywine Blue Gneiss. The Brandywine Blue Gneiss is the new name given to the granulite-facies felsic gneisses in the Wilmington Complex. Informally called the âblue rocks,â this unit is a medium- to coarse-grained, lineated (pinstriped), two-pyroxene gneiss with variable quartz content and thin, discontinuous mafic layers, pods, and schlieren. The pinstriping and the massive nature of the rock suggest the rock is intrusive; however, deformation and recrystallization have obscured original igneous features.
The unit appears on the Wilmington North, Wilmington South, and Marcus Hook quadrangles where it underlies the city of Wilmington and its northeastern suburbs.
Seismometer:Mark Products L-4C Short period Vertical
Amplifier: Sprengnether AS-110 Gain 68dB
VCO: TC-10 1700 Hz
Elevation: 58 meters above sea level
Brandywine Creek State Park (BWD) Seismic StationBrandywine Creek State Park (BWD) Seismic Station johncallahan Tue, 07/28/2009 - 00:59
The seismometer located at Brandywine Creek State Park is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.
The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East quadrangles.
Seismometer: HS101-A Short period Vertical
Amplifier: Emtel 6243 Gain 36dB
VCO: 2720 Hz
Elevation: 63 meters above sea level
Delaware Emergency Management Agency (DEMA) Seismic StationDelaware Emergency Management Agency (DEMA) Seismic Station johncallahan Tue, 07/28/2009 - 14:23
The seismometer, located at the Delaware Emergency Management Agency, is located on the Columbia Formation. The Columbia Formation is a fine to coarse, feldspathic quartz sand with varying amounts of gravel. It is primarily a body of glacial outwash sediment deposited in a cold climate during the middle Pleistocene.
Seismometer:Geospace Corp. HS-10 Short period
Amplifier: Emtel 6242 Gain -18dB
VCO: 2380 Hz
Elevation: 14 meters above sea level
Sussex County Emergency Operation Center (SCOM) Seismic StationSussex County Emergency Operation Center (SCOM) Seismic Station johncallahan Tue, 07/28/2009 - 14:30
The seismometer, located on the property of the Sussex County Emergency Operation Center, is positioned on the Beaverdam Formation. The Beaverdam Formation is a very coarse sand with beds of fine to medium sand. It is interpreted to be a Pliocene fluvial to estuarine deposit.
Seismometer: Geospace Corp HS-10-1/B Short period Vertical
Amplifier: Emtel 6242 Gain -18dB
VCO: 1020 Hz
Elevation: 15 meters above sea level
White Clay Creek State Park (NED) Seismic StationWhite Clay Creek State Park (NED) Seismic Station johncallahan Tue, 07/28/2009 - 13:58
The seismometer, located in White Clay Creek State Park, is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.
The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East U. S. Geological Survey 7.5-minute quadrangles.
Seismometer:Teledyne Geotech S-13 Short period Vertical
Amplifier: Emtel 6243 Gain 24dB
VCO: 2380 Hz
Elevation: 90 meters above sea level
Greenville (GEDE) Seismic StationGreenville (GEDE) Seismic Station johncallahan Wed, 10/01/2014 - 11:46
The seismic instruments located at the Greenville, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.
The equipment at this station was installed on 2013-04-28.
For more info, visit the station page at the Array Network Facility.
- Quanterra Q330 Datalogger
- Streckeisen STS-2 Broadband Seismometer
- Setra 278 Microbarometer
- NCPA Infrasound Microphone
- MEMS Barometric Pressure Gauge
Elevation: 110 meters (NAVD88)
Milford (MIDE) Seismic StationMilford (MIDE) Seismic Station johncallahan Wed, 10/01/2014 - 12:07
The seismic instruments located at the Milford, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.
The equipment at this station was installed on 2013-05-28.
For more info, visit one of the following sites:
- Quanterra Q330 Datalogger
- Nanometrics Trillium 240 v2 Broadband Seismometer
- Setra 278 Microbarometer
- NCPA Infrasound Microphone
- MEMS Barometric Pressure Gauge
Elevation: 10 meters (NAVD88)
Historical DGS SeismographsHistorical DGS Seismographs siteadmin Wed, 03/01/2017 - 11:22
Stream and Tide Gage Data for Hurricane SandyStream and Tide Gage Data for Hurricane Sandy johncallahan Wed, 10/31/2012 - 15:41
Hurricane Sandy was a major storm event for the tidal areas of Delaware. As a part of the mission of the Delaware Geological Survey, we have compiled preliminary Delaware tide and stream-level data for Hurricane Sandy and compared them with previous flooding records. The following tables are the result of the compilation. Please note that these data are preliminary and are subject to change as the data are verified. We have also included some rainfall data to show the rainfall distribution throughout the state related to the storm. These data were provided by the Delaware State Climatologists Office (http://climate.udel.edu/) and were collected as part of the Delaware Environmental Operating System (DEOS, http://www.deos.udel.edu/). The following map shows the location of the stream and tide gages and the DEOS stations used in this report.
Rainfall data provided by DEOS.
The following table is a summary of the preliminary tidal high water levels produced by Hurricane Sandy. The record high levels prior to Hurricane Sandy, the date of these levels, and the event (storm or hurricane) are shown for comparison. Nine record levels were reached for the tide gages on the Nanticoke River, in the Inland Bays and along the tidal portion of the Delaware River and its tributaries north of the Chesapeake and Delaware Canal. We have also included two NOAA tide gage graphs (at the bottom of this page) from Breakwater Harbor and Reedy Point that show the rise and fall of the tides during the storm. The difference between the predicted tides and the actual tides is the tidal surge that was the result of the storm.
|Hurricane Sandy||Prior Record High|
|Station||Gage Height (ft)||Date||Timez||Gage Height (ft)||Date||Event||Tidal
|Delaware River at Marcus Hook||9.94||10/30/12||3:30||9.76||4/17/11||low pressure system||MLLW||NOAA|
|Christina River at Newport||***8.06||10/30/12||2:18||8.07||9/17/99||Floyd||NGVD 1929||USGS|
|Christina River at Wilmington||8.26||10/30/12||2:36||7.71||4/16/11||low pressure system||NGVD 1929||USGS|
|Delaware River at New Castle||failed during storm||*7.68||5/12/08||Mothers Day Storm||NAVD 1988||USGS|
|Delaware River- Delaware City||9.74||10/30/12||1:54||9.38||4/16/11||low pressure system||MLLW||NOAA|
|Reedy Pt.- Mouth of C&D Canal||9.10||10/30/12||1:42||9.23||4/16/11||low pressure system||MLLW||NOAA|
|Murderkill River at Frederica||4.84||10/29/12||13:18||5.15||5/12/08||Mothers Day Storm||NGVD 1929||USGS|
|Murderkill River at Bowers||4.79||10/29/12||10:36||8.23y||3/3/94||Northeaster||NAVD 1988||USGS|
|Ship John Shoal||9.42||10/30/12||0:12||9.29||4/16/11||low pressure system||MLLW||NOAA|
|Brandywine Shoal Light||failed during storm||8.66||8/27/11||Irene||MLLW||NOAA|
|Breakwater Harbor at Lewes||8.70||10/29/12||9:36||9.22||3/6/62||March '62 Storm||MLLW||NOAA|
|Indian River Inlet||**6.51||10/29/12||9:54||**5.86||2/5/98||Northeaster||NGVD 1929||USGS|
|Indian River at Rosedale||6.23||10/29/12||10:48||6.99||2/5/98||Northeaster||NGVD 1929||USGS|
|Rehoboth Bay at Dewey Beach||5.34||10/29/12||22:30||4.45||10/31/99||Halloween Northeaster||NGVD 1929||USGS|
|Jefferson Creek at South Bethany||5.44||10/30/12||0:42||3.52||9/19/03||Isabel||NGVD 1929||USGS|
|Little Assawoman Bay||4.82||10/30/12||0:00||3.13||10/25/05||Wilma||NGVD 1929||USGS|
|Nanticoke River at Sharptown||5.59||10/30/12||4:36||4.11||3/3/94||Northeaster||NGVD 1929||USGS|
|*||gage malfunction, reading may be spurious|
|**||data erratic, high winds and waves|
|***||no data collected between 2:18 and 4:18 EDT during peak tide|
|y||previous tide gage, record for the present gage is 7.8 ft for the Mothers Day storm 5/12/08|
|9.94||red and bold indicates new record high|
|z||Eastern Daylight Time|
Although significant rainfall occurred throughout Delaware and in southeastern Pennsylvania, no new record stream levels were recorded. Flood stage was reached on five of the streams in northern Delaware. The levels shown in the following table are typical for a heavy rainfall event. We have also included three USGS hydrographs (at the bottom of this page) from the Brandywine at Wilmington, Red Clay Creek near Stanton, and White Clay Creek near Newark streamgages that show the rising water levels in the streams during the storm. It is possible or even likely that in areas in the Coastal Plain of Delaware where rainfall was the heaviest that small streams and ditches may have had significant flooding but no stream gages are located in these areas to record the event.
|USGS Station||Hurricane Sandy
Gage Height (ft)
|Flood Stage (ft)||Record
Gage Height (ft)
|Brandywine Crk at Wilm||16.66||16.50||*18.71||Hurricane Irene 2011|
|Shellpot Creek||5.78||8.00||13.76||Thunderstorm 1989|
|Red Clay Creek at Woodale||>7.45**||7.50||17.62||TS Henri 2003|
|Red Clay Creek near Stanton||17.00||16.00||25.52||TS Henri 2003|
|White Clay Creek at Newark||9.84||11.50||17.13||Hurricane Floyd 1999|
|White Clay Creek near Newark||15.12||13.50||*17.57||Hurricane Floyd 1999|
|Christina River at Cooch's Bridge||12.35||10.50||13.73||Hurricane Floyd 1999|
|St. Jones River at Dover||7.70||-||11.72||Hurricane Irene 2011|
|Nanticoke River at Bridgeville||8.25||-||10.31||1979|
|*||Record gage height at curent gage location|
|**||Highest recorded value before going out of service during the storm|
About the gages, stream and tide data
The Delaware Geological Survey (DGS) is actively involved in the monitoring of natural hazards such as stream and tidal flooding that are the result of large storms. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising both county and state emergency management agencies on natural hazards. The DGS serves on the Delaware Emergency Management Agencyâ€™s (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and had staff located at the Delaware Emergency Operations Center during Hurricane Sandy. An important component of monitoring storm events is having a real-time stream and tide gage network. These gages allow for monitoring of flooding during a storm as it happens to provide information to emergency managers and responders regarding areas of flooding and areas that may be flooded given the trends of rising stream or tide levels. The US Geological Survey, in cooperation with the Delaware Geological Survey, through a Federal-State partnership program operates and maintains stream and tide gages throughout Delaware. Funding for operation and maintenance of this partnership program is provided by the Delaware Geological Survey, US Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Emergency Management Agency, City of Wilmington, City of Newark, and United Water Delaware. The National Oceanic and Atmospheric Administration (NOAA) maintains tide gages in the Delaware Bay and River for purposes of navigation safety, environmental stewardship, and environmental assessment and prediction. These gages are an invaluable resource for real-time tidal conditions in the Delaware Bay and River.
- Hurricane Sandy information from the Delaware State Climatologist
- Hurricane Sandy Q&A from UDaily
- Northeast US Crisis Map from Superstorm Sandy (Google)
- NOAA Hurricane Sandy Response Imagery Viewer
- USGS Flood and Tidal Data for Hurricane Sandy, including Storm Tide Mapper
For more information on Delaware flooding due to Hurricane Sandy, please contact Kelvin Ramsey at the Delaware Geological Survey (firstname.lastname@example.org, 302-831-2833.) For rainfall totals, please contact the Delaware State Climatologist Office.