Images

Photo of bridge.  Geotechnical means referring to the use of scientific methods and engineering principles to acquire, interpret, and apply knowledge of earth materials for solving engineering problems.  

Horst and graben diagram. A graben is a down-dropped block of the earth's crust resulting from extension, or pulling, of the crust. 

Iceland and plate motions. Kinematic refers to the general movement patterns and directions of the earth's rocks that produce rock deformation.

Plot showing least squares fit. When plotting data points on a graph, the least-squares-fit is the line or curve that comes closest to going through all the points.

The Landers fault (red lines at left) and the Hector Mine fault and its aftershocks (red lines and circles at right). The Hector Mine earthquake was a magnitude 7.1, and it produced thousands of aftershocks.

The natural frequency is the frequency at which a particular object or system vibrates when pushed by a single force or impulse, and not influenced by other external forces or by damping. If you hold a slinky by one end and let it hang down and then give it one push up from the bottom, the rate of up-and-down motion is its natural frequency.

A P wave, or compressional wave, is a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving.

Diagram of period.  The period is the time interval required for one full cycle of a wave.

Moment = ? A D

? = shear modulus = 32 GPa in crust, 75 GPa in mantle

A = LW = area

D = average displacement during rupture

The New Madrid seismic zone in Central U.S.

A seismic zone is an area of seismicity probably sharing a common cause. 

A seismogram is a record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.

A slab is the oceanic crustal plate that underthrusts the continental plate in a subduction zone and is consumed by the earth's mantle.

This turn-of-the-century wooden residence in Los Gatos sustained major damage when it moved off its foundation during the October 17, 1989, M7.1 Loma Prieta, California earthquake.

A surface wave is a seismic seismic wave that is trapped near the surface of the earth.

A tsunami is a sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands.

Figure 2.

Figure 1. Chance of minor or greater damaging earthquake shaking in the next 100 years. Population exposure estimates are rounded to the nearest 1000. 

Seismicity of Hawaii: earthquakes M>5 from the 1840-1899, 1900-1959, 1960-2019 catalogs shown separately. While earthquake activity remains high today, it seems to have decreased over the past 60 years, which could be related to less volcanic activity at Mauna Loa. 

Debris flow caused by intense rainfall from Tropical Storm Fred in August 2021. Haywood County, NC. 

2018 Long-term National Seismic Hazard Map. Earthquake hazard map showing peak ground accelerations having a 2 percent probability of being exceeded in 50 years, for a firm rock site.  The map is based on the most recent USGS models for the conterminous U.S.

Debris flow deposits caused by intense rainfall in April 2020 block a highway in Macon County, NC.