Geophysics the use of geology, laboratory & field experiments, mathematics, and instruments to study: Earthquakes and Volcanoes seismometers, tiltmeters, EDM, remote sensing, Energy: oil, gas, hydrothermal seismic reflection and refraction, boreholes Environment: water, minerals electromagnetic resistivity, Earth Structure and Geodynamics Global Positioning System (GPS)
Active and Passive Source seisms are used to study the Earth -Passive Source record naturally occurring seisms such as earthquakes - Active Source we generate a seism (source) and record the signals (returns) that reflect or refract from the earth materials http://www.iris.edu/data/seismograms/ This is based on the simple mathematics of Rate (R) = distance (d) divided by time (t) R = d/t
Geophysical experiments can be conducted in different locations: > Terrestrial - using geophones and seismometers to record earthquakes or seismic signals. > Ocean using ocean Bottom Seismometers (OBS) to record earthquakes on the seafloor > Extra-terrestrial to record Moonquakes or meteor impacts (passive), or spent rocket collisions (active) to calibrate seismometers on the Moon or Mars or...?
Seismic Array Networks in the United States
Seismic Array Networks in Antarctica
A typical field Seismic station Seismic stations in extreme environments (e.g. Antarctica) need special equipment
or extra terrestrial equipment. Detected Moonquakes at the lithosphere-aesthenosphere boundary, about 1000-km deep that peak during the monthly lunar cycle, with magnitudes of 0.5 to 1.3 Deployment of the lunar seismometer during the Apollo 11 moon Mission, July 1969 returned data for only 3-weeks!
Trinidad, California has a water problem. Too many people using too much water, which is flushing through the system, and showing up at the beach. Geophysics is used to help mitigate the problem.
Collecting Geophysical data in Trinidad in order to mitigate the waste water discharge issue. geophones Data logger Coaxial cable
Seismic Reflection data for Profile 1
Electromagnetic Resistivity data for Profile 1
Seismic Reflection data for Profile 3
Electromagnetic Resistivity data for Line 3
Seismic Reflection data for Profile 4
Electromagnetic Resistivity data for Line4
Continental Margins are the edges of the continents where the land meets the sea Continental Shelf: flat part of the margin that extends from the shore to about 150-meters water depth Continental Slope: the steeper part of the margin that slopes down to the Abyss about 2000-meters depth Abyssal Plains: the deep ocean and some of the flattest places on earth deep, dark, cold, crushing pressure Active Margins: typically narrow (~10-km), many faults, large earthquakes, volcanic arcs, trenches, submarine landslides are common Passive Margins: wider (200-km), thick sediments, earthquakes are uncommon, no trench, but submarine landslides occur here too
Submarine Landslides or Turbidity Currents: Gravity driven flows that occur where sediment builds up and flow down the continental slope onto the abyssal plains. Triggered as result of over-steepening, earthquake or seafloor instability and may generate tsunami http://www.activetectonics.coas.oregonstate.edu/model_turbs.htm
Sequence Stratigraphy is a model of how continental margin respond to sea level rise. Sediments are delivered from the upland regions (rivers) and fill in basins (oceans and lakes). The sequence boundary is the surface during low-sea levels (glacial periods) and the arrows represent how the sediments fill the basin.
Sequence stratigraphic model of a Passive margin (no trench). LST is Low Stand Tract (glacial period): ~ 20,000 years ago HST is High Stand Tract (inter-glacial period) = modern times
Active Source SONAR Chirp 1Hz 10Hz 100 Hz 1Khz 10kHz 100KHz 1MHz 10MHz 100MHz 1GHz 10GHz Frequency Range (cycles per second)
SONAR Mapping Tools
Seafloor mapping using SONAR
Multi-beam swath bathymetry map of northern Humboldt Continental Shelf
Chirp Sonar 0.6 500 khz
Core Q-45 collected on the anticline west of Humboldt Bay. Coarse sand over fine grained mud indicates an abrupt change in the environment.