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Quake hunting. Mars lacks the tectonic plates that produce the temblors many people in seismically active areas are familiar with. But there are two other types of quakes on earth that also occur on Mars. Those caused by rocks cracking under heat and pressure and those caused by meteoroid impacts. The two types of meteoroid impacts on Mars produce high frequency seismic waves that travel from the crust deep into the planet's mantle according to a paper published earlier this year in Geophysical Research Letters. Located beneath the planet's crust, the Martian mantle can be as much as 960 miles or about 1550 kilometers thick. It is made of solid rock that can reach temperatures as high as 2732 degrees Fahrenheit or about 1500 degrees Celsius. Scrambled signals. The new science paper identifies eight Mars quakes whose seismic waves contain strong high frequency energy that reach deep into the mantle where their seismic waves were distinctly altered. When we first saw this in our quake data, we thought the slowdowns were a powerful distraction cross-plate set. But then we noticed that the farther seismic waves traveled through the mantle, the more these high frequency signals were being delayed. In Planetwide Computer Simulations, the team saw that the slowing down and scrambling happened only when the signals passed through small localized regions within the mantle. They also determined that these regions appeared to be lumps of material with a different composition than the surrounding mantle. With one riddle solved, the team focused on another, how these lumps got there.