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: 10.00 km ( = 6.21 miles )

Projectile diameter: 800.00 meters ( = 2620.00 feet )

Projectile Density: 1500 kg/m³

Impact Velocity: 11.30 km per second ( = 7.00 miles per second )

Impact Angle: 45 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 2.55 x 10¹⁹ Joules = 6.10 x 10³ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.8 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 65900 meters = 216000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 11 km/s = 6.85 miles/s

The energy lost in the atmosphere is 1.07 x 10¹⁸ Joules = 2.55 x 10² MegaTons.

The impact energy is 2.45 x 10¹⁹ Joules = 5.85 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 1.61 km by 1.14 km

Crater Dimensions:

What does this mean?

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

Transient Crater Diameter: 5.83 km ( = 3.62 miles )

Transient Crater Depth: 2.06 km ( = 1.28 miles )

Final Crater Diameter: 7.38 km ( = 4.58 miles )

Final Crater Depth: 540 meters ( = 1770 feet )

The crater formed is a complex crater.

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 2 seconds after impact.

Richter Scale Magnitude: 7.1

Mercalli Scale Intensity at a distance of 10 km:

IX. General panic. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters.

X. Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.

Ejecta:

What does this mean?


The ejecta will arrive approximately 45.2 seconds after the impact.

Your position is beneath the continuous ejecta deposit.

Average Ejecta Thickness: 10.3 meters ( = 33.9 feet )

Mean Fragment Diameter: 20.6 meters ( = 67.6 feet )

Air Blast:

What does this mean?


The air blast will arrive approximately 30.3 seconds after impact.

Peak Overpressure: 2.62e+06 Pa = 26.2 bars = 372 psi

Max wind velocity: 1270 m/s = 2850 mph

Sound Intensity: 128 dB (Dangerously Loud)

Damage Description:

Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Highway girder bridges will collapse.

Glass windows will shatter.

Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

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.