Earth Impact Effects Program

Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:

Distance from Impact: 100.00 km ( = 62.10 miles )

Projectile diameter: 500.00 meters ( = 1640.00 feet )

Projectile Density: 3000 kg/m³

Impact Velocity: 9.00 km per second ( = 5.59 miles per second )

Impact Angle: 90 degrees

Target Density: 1000 kg/m³

Target Type: Liquid water of depth 2.5 km ( = 1.6 miles ), over crystalline rock.

Energy:

Energy before atmospheric entry: 7.95 x 10¹⁸ Joules = 1.90 x 10³ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.4 x 10⁵years

Major Global Changes:

The Earth is not strongly disturbed by the impact and loses negligible mass.

The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).

The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:

The projectile begins to breakup at an altitude of 43900 meters = 144000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 8.91 km/s = 5.53 miles/s

The energy lost in the atmosphere is 1.62 x 10¹⁷ Joules = 3.87 x 10¹ MegaTons.

The impact energy is 7.79 x 10¹⁸ Joules = 1.86 x 10³MegaTons.

The larger of these two energies is used to estimate the airblast damage.

The broken projectile fragments strike the ground in an ellipse of dimension 0.632 km by 0.632 km

Crater Dimensions:

What does this mean?

The crater opened in the water has a diameter of 8.3 km ( = 5.15 miles ).

For the crater formed in the seafloor:

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 1.93 km ( = 1.2 miles )

Transient Crater Depth: 684 meters ( = 2240 feet )

Final Crater Diameter: 2.42 km ( = 1.5 miles )

Final Crater Depth: 514 meters ( = 1690 feet )

The crater formed is a simple crater

The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 238 meters ( = 782 feet ).

At this impact velocity ( < 12 km/s), little shock melting of the target occurs.

Thermal Radiation:

What does this mean?

At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 20 seconds after impact.

Richter Scale Magnitude: 5.5

Mercalli Scale Intensity at a distance of 100 km:

III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck.

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

Ejecta:

What does this mean?


The ejecta will arrive approximately 2.4 minutes after the impact.

At your position there is a fine dusting of ejecta with occasional larger fragments

Average Ejecta Thickness: 125 microns ( = 4.91 thousandths of an inch )

Mean Fragment Diameter: 1.46 cm ( = 0.575 inches )

Air Blast:

What does this mean?


The air blast will arrive approximately 5.05 minutes after impact.

Peak Overpressure: 11900 Pa = 0.119 bars = 1.7 psi

Max wind velocity: 26.8 m/s = 60 mph

Sound Intensity: 82 dB (Loud as heavy traffic)

Damage Description:

Glass windows will shatter.

Tsunami Wave:

What does this mean?

The impact-generated tsunami wave arrives approximately 12.1 minutes after impact.

Tsunami wave amplitude is between: 2.7 meters ( = 8.8 feet) and 48.2 meters ( = 158.0 feet).

Click here for a pdf document that details the observations, assumptions, and equations upon which this program is based. It describes our approach to quantifying the important impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The processes included are: atmospheric entry, impact crater formation, fireball expansion and thermal radiation, ejecta deposition, seismic shaking, and the propagation of the atmospheric blast wave.

Recent improvements in the airblast calculation are described here.