Cardset

p wave ist schneller

Vektor senkrecht zu Wellenfront.

Zeigt in Ausbreitungsrichtung

hooks law

(Kraft und Auslenkung hängen linear zusammen

mit mass density und stiffness

Anzahl an Punkten mit der selben Phase (in seis. Wellen)

In seismics reflections occur

where the density or the elastic properties

change. The relevant quantitiy is called

Impedance

(In radar reflections occur where the dielectric

properties change)

Large impedance changes cause large

reflections amplitudes (and small transmission).

Small impedance changes cause small reflection

amplitudes (and large transmission).

Reflections can also initiate mode conversions

turning, e.g., initiating an s-wave from an

incoming p-wave.

Reflection amplitudes are also dependent on the

incidence angle etc.

Seismik: nahe und ferne Untersuchungen, teuer

Radar: Nahe Untersuchungen, günstiger

• Öl, Gas

• Baugrund

• Geothermie

• Nukleares Endlager

Wissenschaftlich:

• Mantel convection

• Subduktionszonen

• Eis shelves

• Günstig

• Passiv

• Größere Gebiete einfacher zu untersuchen als mit Seismik

Jeder Punkt auf einer Wellenfront ist der Ausgangspunkt einer weiteren Welle.

The Earth’s magnetic field is time variable, on

contemporary timescales because of solar

storms. Space weather is a real thing and can be

detected, e.g., with GPS measurements. A

reference station in magnetics is more important

than in the gravity method.

• Weak mini-dipoles induced, opposing external field (k < 0).

• Diappears if external field is removed.

• Occurs essentially in all materials, but is not noted everywhere, due to other effects.

• Examples: Quarzite, Calcite, ...

• Advantages: No basestation required

• Advantages: More sensitive to horizontal boundaries

• Advantages: Less sensitive to large-scale patterns

• Advantage/Disadvantage: Sensitive to near-surface structures (=.

• Relevant for applied exercises.

• Nur Vergleichsmessungen zwischen Messpunkten.

• Keine absoluten Messungen

• Advantage: Positioning not so important

• Advantage: Sensitivity < 0.1 nT

• Disadvantage: Base station required (sometimes).

• Disadvantage: Measurement time > 1s

• Related techniques: MRI imaging in medicine

• Material exhibits pre-existing dipoles which orient themselves in external field (unpaired electrons).

• Reinforce external field (k > 0). (magnetic susceptibility is positive)

• Effect dissipates due to thermal fluctuations once external field is removed.

• Examples: gold, copper,...

• Induced: Usually parallel to external field; it disappears if external field disappears; quantified by susceptibility (para-, dia- magnetisme)

• Remanent: Orientation dependent on history; temporally persistent; occurs in ferromagnetic materials with large magnetic domains.

  -> dadurch auch mal nicht parallel zu Erdmagnetfeld, zB MOR

• Thermoremanent magnetization: cooling below Curie Temperature in igneous Rocks

• Detrital magnetization: slow setteling of fine-grained materials (clay)

• Lightning Strike induced: (should occur within lighting belt)

Wie sich Materialien bei einem externen mag. Feld verhalten

Magnetik misst oft in 3D

-> Mehr interpretationen

Gleiches Prinzip bei Leitfähigkeit / spezifische Leitfähigkeit

• Müllhalden finden

• Kontaminationen

• …

Solution to overcome the contact resistance at electrodes A, B:

• Measure the potential drop with two different electrodes (M,N) at a different location and without injecting a current (i.e. the contact resistance is then unimportant.)

Im Untergrund sind keine Kabel -> alles ungerichtet

K: Konfigurationsfaktor

Ohms law umgeformt für resistivity

• Wenner: Sensitiv zu vertikal

• Schlumberger: sensitiv zu lateral

K: Konfigurationsfaktor

• Install two sensors at different heights (e.g., vertical fluxgates 0.5 m apart).

• Consider only the vertical gradient.

• Insensitive to the total field and temporal variability thereof.

• Sensitive to near-surface structures (why?).

• Sensitive to horizontal boundaries.

• Relevant for applied exercises.

metall. leitung in zB Kabeln

Ionische Leitung bei Resistivity Methode (zB. Wasserionen)

Äquator

Nordpol

Südpol

45 Breitengrad

Tübingen

• Material exhibits pre-existing dipoles which are oriented in domains with strong coupling.

• Domains align and strongly reinforce external field ( k>> 0). -> positive and very strong

• Effect can be maintained if external field is removed.

• Examples: iron, nickel, ...

• wie tief will ich messen

• was für einen Abstand brauche ich dann

• Anzahl der Messungen

• Kabel/ Kosten

Radar ist vergleichbar mit reflektionsseismik, eher nicht mit refraktionsseismik!