Twinning Definition Twinning is the observed intergrowth of multiple crystals in a symmetrical fashion. This term applies to the examination of rock thin sections, in the field of optical mineralogy.

Geosyncline Geosyncline: In geology, a geosyncline is a large-scale indentation in the Earth’s crust that is filled with sediments. A geosyncline forms due to the gradual sinking of the Earth’s crust, causing sediment from adjacent areas to gather inside. An example of a geosyncline is the Appalachian Mountains.

Asthenosphere Asthenosphere: The asthenosphere underlies the lithosphere. The Asthenosphere comprises the upper mantle, where isostatic adjustments are made, and where magma is generated. It is also in this part of the earth, where seismic waves strongly attenuate.

Licensed Professional Geologist A “Licensed Professional Geologist” or a “Certified Professional Geologist” is a person who is certified by a State and/or Federal agency (such as the California Department of Consumer Affairs, Board for Professional Engineers, Geologists & Land Surveyors), and has proven be educated, formally trained and professionally competent per government standards, to practice…

Effective Size (D10) “Effective Size” (D10) is an engineering geology term. Effective Size represents a diameter that directly corresponds to the percentage, by weight, of grains that equal to 10% on the grain-size diagram. To illustrate, 10% of the soil sample particles are finer-grained, and 90% of the sample particles are coarser than the “effective…

Fault Creep Fault Creep: Fault creep means slow ground displacement of a strike-slip fault or dip-slip fault, that usually occurs without accompanying earthquakes. Fault creep can derive from tectonic activity, or be the result of excessive petroleum and groundwater pumping.