### motion | vibration:

Random vibration
* contains no periodic or quasi-periodic constituents.
* has a histogram that has a bell-curve shape.

Slower vibration
* equate to lower-frequency sounds.
* have less heat.

Sound vibration
* Most sound vibration creates sound waves
* Some sound vibration moves through air.
* enter the ear canal and cause the eardrum to vibrate.
* extend from a few cycles per second to millions of cycles per second.
* have different frequencies.
* travel at different speeds through different materials
  - in waves that can be measured based on intensity and frequency

### motion | vibration:

Tremor
* Most tremors occur in the hands.
* Some tremors respond to treatment of the underlying condition.
* are a type of dyskinesia
  - shaking movement
  - earthquakes
  - involuntary shaking of arms or legs
  - less likely if the dose is increased slowly, rather than rapidly
  - rhythmic shaking movements of the hands, lower arms, and head
  - small earthquakes that are common in Japan
  - usually the first symptom of mercury toxicity
  - vibes
* can also occur in the head, lips, tongue and feet
  - be an indication of hypoglycemia , along with palpitations, sweating and anxiety
* continue throughout El Salvador, and are causing new landslides to occur.
* disappear when the affected limb is in motion and while the patient sleeps.
* is about our inner and outer fault lines
* jiggle the springs, which move the wires inside the core to produce an electrical current.
* occur as a result of damage to the nerve cells
  - at any age but are most common in older people
  - from contractions of different, often opposing, muscle groups
  - when the arm or leg is relaxed and disappear when they are in use
* often begin on one side of the body, frequently in one hand.
* usually disappear during sleep and increase under stress.

### motion | vibration | tremor:

Aftershock
* actually become less frequent with time, rather than smaller, as is commonly believed.
* are as small earthquakes which come immediately after an earthquake
  - common with earthquakes
* are earthquakes that usually occur near the mainshock
  - themselves and can be as severe as the original temblor
  - formed as the crust adjusts to the effects of the main shock
  - larger than the main shock in an earthquake sequence
* can level severely damaged buildings.
* can occur for several months, with tremors gradually becoming smaller
  - in the first hours, days, weeks, or even months after the quake
* decrease in number and magnitude over time.
* differentiate earthquakes from other natural disasters.
* exhibit a particular pattern with time.
* frequently occur minutes, days, weeks and even months following an earthquake
  - weeks, and even months
* normally occur a few days after a major quake.
* occur in the following days to weeks.
* often follow after an earthquake
  - occur after quakes and can cause weakened structures to fall down
+ Earthquake, Earthquake clusters, Aftershocks: Plate tectonics
  * An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. Aftershocks are formed as the crust adjusts to the effects of the main shock.

### motion | vibration | tremor | aftershock:

Large aftershock
* can cause significant damage and loss of life.
* tend to occur sooner rather than later.